Latest / Night Science Stories / Neuroscientists Still Don’t Know Why We Dream The Sleepy Scientist

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Neuroscientists Still Don’t Know Why We Dream The Sleepy Scientist · Night Science Stories

0:01
Speaker 1: One small thing before we begin. If you regularly fall
0:05
Speaker 1: asleep to these videos, there's a good chance your phone
0:08
Speaker 1: spends the entire night awake beside you, screen glowing away
0:12
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0:15
Speaker 1: a slightly better arrangement. The Sleepy Scientist is on Spotify.
0:20
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0:24
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0:27
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0:30
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0:35
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0:38
Speaker 1: a five-star rating would be hugely appreciated. It really does
0:41
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0:44
Speaker 1: the description. Right then, get comfortable. Phone down. Worries temporarily postponed.
0:59
Speaker 2: Good evening. and welcome to the Sleepy Scientist. It's lovely
1:03
Speaker 2: to have you here tonight. I'm always curious where these
1:06
Speaker 2: evenings end up, so if it's not too much to ask,
1:08
Speaker 2: do leave me a comment and tell me where in
1:10
Speaker 2: the world you're listening from. A dark bedroom. A room
1:14
Speaker 2: where you've already stopped properly keeping track of the time.
1:17
Speaker 2: A kitchen table, long after the dishes were done. Wherever
1:21
Speaker 2: you are, I hope you're warm, comfortable and ready to
1:24
Speaker 2: let the day drift away. If you'd rather listen with
1:28
Speaker 2: the screen off, you'll find us on Spotify, and there's
1:30
Speaker 2: a link in the description. Close your eyes whenever you like.
1:34
Speaker 2: I'll carry on talking either way. And if you enjoy
1:37
Speaker 2: these slow wanderings through science, a like and a subscribe,
1:42
Speaker 2: help this little channel drift a bit further out into
1:45
Speaker 2: the world. Best to do it while you're still awake
1:48
Speaker 2: enough to decide to. If you're already with us, thank you.
1:52
Speaker 2: Your company on these evenings means a great deal. Now,
1:56
Speaker 2: I'll do my best not to make tonight's subject so
1:59
Speaker 2: interesting that it keeps you awake. Although consciousness is a
2:03
Speaker 2: slightly awkward one for a sleep channel, given that the
2:06
Speaker 2: whole evening is heading gently towards the moment when yours
2:09
Speaker 2: switches off, and that's part of what makes it so strange.
2:13
Speaker 2: Right now, there's a voice in your ears, perhaps some
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Speaker 2: darkness behind your eyelids, perhaps a thought about something else entirely,
2:21
Speaker 2: which arrived without being invited. Somehow, There is an experience happening,
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Speaker 2: and it's happening from your point of view and nobody else's.
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Speaker 2: Science can tell us an extraordinary amount about the brain
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Speaker 2: producing all this. We can watch individual cells firing. We
2:39
Speaker 2: can follow signals racing through the network. We can switch
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Speaker 2: the whole thing off with anaesthetic and watch it come
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Speaker 2: quietly back on again afterwards. But one question stays stubbornly
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Speaker 2: out of reach. Why does any of that feel like
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Speaker 2: anything at all? Why isn't it all just happening in
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Speaker 2: the dark? So, shall we begin? What is consciousness, and
3:00
Speaker 2: how does a lump of physical matter create the experience
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Speaker 2: of being you? There is something rather strange about the
3:08
Speaker 2: way a dream disappears. You can wake with the unmistakable
3:12
Speaker 2: feeling that, only moments ago, you were somewhere else entirely.
3:17
Speaker 2: Perhaps you are walking through a city that does not exist,
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Speaker 2: talking to someone you have not seen for years, trying
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Speaker 2: to catch a train from a station built inside your
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Speaker 2: old school, while somehow accepting all of this as perfectly reasonable.
3:32
Speaker 2: There may have been fear, excitement, embarrassment, relief, or the
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Speaker 2: peculiar seriousness that dreams give to situations which would make
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Speaker 2: absolutely no sense in daylight. And then, within seconds, it
3:48
Speaker 2: begins to go. A face disappears first, then the locations.
3:54
Speaker 2: then whatever problem seemed terribly important while you were asleep.
3:59
Speaker 2: You may still remember that something happened, perhaps even something elaborate,
4:04
Speaker 2: but the details retreat so quickly that trying to hold
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Speaker 2: on to them can feel like trying to remember a
4:09
Speaker 2: conversation heard through a wall. By breakfast, much of it
4:14
Speaker 2: may be gone entirely. Across a typical night, an adult
4:18
Speaker 2: can spend roughly a couple of hours in rapid eye
4:21
Speaker 2: movement sleep. although the exact amount varies with age, sleep
4:25
Speaker 2: duration and the individual. Rapid eye movement sleep becomes especially
4:30
Speaker 2: prominent during the later part of the night, which is
4:33
Speaker 2: one reason vivid dreams are often noticed close to morning.
4:37
Speaker 2: But dreaming and rapid eye movement sleep are not the
4:40
Speaker 2: same thing. That distinction is important. For many years, rapid
4:45
Speaker 2: eye movement sleep and dreaming became so closely associated that
4:49
Speaker 2: they were sometimes treated almost as interchangeable. Researchers now know
4:54
Speaker 2: that people can report dream experiences after being awakened from
4:57
Speaker 2: several different stages of sleep. Dreams occurring during rapid eye
5:02
Speaker 2: movement sleep are often especially vivid, emotional and elaborate. But
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Speaker 2: the sleeping mind does not suddenly stop producing experiences whenever
5:11
Speaker 2: rapid eye movement sleep ends. At its simplest, a dream
5:15
Speaker 2: is a subjective experience produced while a person is asleep.
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Speaker 2: That experience might contain pictures, Voices, movement, thoughts, emotions, bodily sensations,
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Speaker 2: memories or an apparent sense of occupying a completely different place.
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Speaker 2: Some dreams resemble complicated films. Others consist of little more
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Speaker 2: than a thought, an image, a feeling or a fragment
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Speaker 2: of conversation. The remarkable part is that the real bedroom
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Speaker 2: has not gone anywhere. Your eyes are closed. Information arriving
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Speaker 2: from the outside world has been greatly reduced. Your body
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Speaker 2: may be lying almost motionless beneath a duvet. Yet inside
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Speaker 2: the sleeping brain, another environment can temporarily take priority. A
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Speaker 2: person can feel as though they are running while their
6:05
Speaker 2: legs remain still. They can hear speech when nobody in
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Speaker 2: the room is talking. They can see bright daylight in
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Speaker 2: complete darkness. They can meet people who died years ago and,
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Speaker 2: at least for a while, find nothing particularly suspicious about it.
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Speaker 2: Dreaming is therefore different from simply deciding to imagine something
6:26
Speaker 2: while awake. If you imagine a beach right now, the
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Speaker 2: imagined beach normally exists alongside your awareness of the room
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Speaker 2: around you. You know that you are creating an image.
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Speaker 2: The sounds, pressure, temperature and visual information of the real
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Speaker 2: environment remain available. During a vivid dream, that balance can
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Speaker 2: change dramatically. External sensory information is reduced. while internally generated
6:52
Speaker 2: activity becomes convincing enough to form the experienced world. This
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Speaker 2: creates an unusual problem for scientists. A sleeping brain can
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Speaker 2: be measured in extraordinary detail. Researchers can record electrical activity
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Speaker 2: from the scalp. They can observe eye movements. They can
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Speaker 2: measure breathing, heart rate and muscle tone. Brain imaging can
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Speaker 2: reveal which regions become more or less active during different
7:16
Speaker 2: states of sleep. What cannot currently be placed on a
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Speaker 2: laboratory monitor is the dream itself. The researcher sees signals.
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Speaker 2: The dreamer sees the impossible city. Everything scientists learn about
7:29
Speaker 2: dream experience therefore depends, at some point, on connecting measurable
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Speaker 2: events in the sleeping body with what the person reports
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Speaker 2: after waking. And that creates an unavoidable delay. The experience
7:42
Speaker 2: has already happened by the time it can be described.
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Speaker 2: Even then, memory becomes part of the problem. Dreams are
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Speaker 2: often forgotten extraordinarily quickly. One reason may be that the
7:53
Speaker 2: neurochemical environment of sleep is not especially favourable to forming
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Speaker 2: the same kind of durable memories produced during ordinary wakefulness.
8:03
Speaker 2: During rapid eye movement sleep, activity in several memory-related systems
8:08
Speaker 2: differs substantially from the waking state, while levels of neurotransmitters
8:13
Speaker 2: involved in attention and memory also change. So the strange
8:17
Speaker 2: vanishing act in the morning may not mean a dream
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Speaker 2: contained very little. It may mean that the brain was
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Speaker 2: poor at storing the experience in a form that could
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Speaker 2: later be retrieved. This difficulty becomes even greater when we
8:31
Speaker 2: ask why dreaming exists. It is much easier to demonstrate
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Speaker 2: that dreaming happens than to demonstrate what dreaming is for.
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Speaker 2: Suppose researchers discover that certain memories are being reorganised during
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Speaker 2: sleep That does not automatically mean dreams exist in order
8:48
Speaker 2: to reorganise memories. The memory processing and the dream might
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Speaker 2: be related, or the dream could simply be what some
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Speaker 2: of that neural activity feels like from the inside. The
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Speaker 2: same caution applies to emotion. Dreams often contain emotionally powerful events,
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Speaker 2: and sleep is involved in several processes associated with emotional regulation.
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Speaker 2: But finding emotion inside dreams does not by itself prove
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Speaker 2: that the biological purpose of dreaming is to regulate emotion.
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Speaker 2: Dreaming may not even have one single purpose. Some aspects
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Speaker 2: could emerge from memory processing. Others may reflect the sleeping
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Speaker 2: brain constructing stories from internally generated signals. Dreams might help
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Speaker 2: simulate possible events, combine fragments of experience, process emotional material,
9:41
Speaker 2: or simply arise because a complex brain continues producing organised
9:45
Speaker 2: conscious experiences, even when largely disconnected from its surroundings. Several
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Speaker 2: of these ideas could be partly correct at the same time,
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Speaker 2: and that may explain why the subject has resisted such
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Speaker 2: tidy answers. Dreaming is incredible. familiar. Human beings have presumably
10:03
Speaker 2: been waking from dreams for as long as human beings
10:06
Speaker 2: have been sleeping. Nearly everyone knows that peculiar morning sensation
10:11
Speaker 2: of returning from somewhere that seemed completely real a few
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Speaker 2: moments earlier. Yet familiarity can hide how extraordinary the event
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Speaker 2: actually is. Every night the brain can build worlds without
10:24
Speaker 2: receiving the ordinary stream of information from the world outside.
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Speaker 2: It can populate them with people, invent conversations, create danger,
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Speaker 2: alter time and geography, and persuade the sleeping mind to
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Speaker 2: accept the result. Then the eyes open, the bedroom returns,
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Speaker 2: and before you have quite worked out where you have been,
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Speaker 2: Much of the evidence has already disappeared. Long before anyone
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Speaker 2: could record electrical activity from a sleeping brain, dreams presented
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Speaker 2: a very different sort of mystery. A person would close
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Speaker 2: their eyes, disappear into sleep, and then find themselves standing
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Speaker 2: before a dead relative, speaking with a god, witnessing a disaster,
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Speaker 2: or wandering through a place they had never seen. In
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Speaker 2: the morning, there was no obvious biological explanation for any
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Speaker 2: of it. There were no brain scans, no sleep laboratories,
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Speaker 2: and no understanding of neurons quietly exchanging electrical and chemical
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Speaker 2: signals through the night. So it was entirely natural to
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Speaker 2: wonder whether the dream had come from somewhere else. Across
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Speaker 2: many ancient cultures, dreams were treated not merely as strange
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Speaker 2: private experiences, but as possible communications. They might contain warnings, predictions, advice,
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Speaker 2: or messages from beings normally hidden from waking life. A
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Speaker 2: vivid dream could therefore feel important in a way that
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Speaker 2: went far beyond an odd memory from the night before.
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Speaker 2: Some of the earlier surviving written discussions of dreams come
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Speaker 2: from ancient Mesopotamia. In societies that developed between the Tigris
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Speaker 2: and Euphrates rivers, dreams could be interpreted as omens sent
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Speaker 2: by gods or as signs pointing towards future events. Kings
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Speaker 2: and other important figures might take a particularly striking dream
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Speaker 2: seriously enough to consult people skilled in interpretation. Dream specialists
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Speaker 2: attempted to work out whether an image promised success, warned
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Speaker 2: of danger, or required some form of ritual response. Dreams
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Speaker 2: also appear prominently in Mesopotamian literature. In the Epic of Gilgamesh,
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Speaker 2: one of the oldest surviving works of literature, dreams repeatedly
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Speaker 2: appear as meaningful experiences requiring interpretation. The details belong to
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Speaker 2: the religious world of the people who created the story,
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Speaker 2: but the underlying human experience is extremely familiar. Someone wakes
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Speaker 2: after a powerful dream and asks the question, people are
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Speaker 2: still asking thousands of years later, what did that mean?
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Speaker 2: Ancient Egyptians developed elaborate traditions of dream interpretation as well.
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Speaker 2: Written dream manuals survive from ancient Egypt in which particular
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Speaker 2: dream experiences were classified as favourable or unfavourable. A person
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Speaker 2: might dream of eating a certain food, looking into water,
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Speaker 2: encountering an animal, or performing an everyday action, and the
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Speaker 2: interpreter would connect that image with some expected outcome. To
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Speaker 2: modern eyes, many of these interpretations appear wonderfully specific. One
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Speaker 2: dream could supposedly signal prosperity while another might announce trouble,
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Speaker 2: often according to associations that made sense within the culture
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Speaker 2: of the time. These manuals tell us something valuable about
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Speaker 2: how seriously dreams could be treated. But they do not
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Speaker 2: demonstrate that the predictions themselves worked. A record showing that
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Speaker 2: people believed dreams could foretell events is evidence about human belief,
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Speaker 2: culture and psychology. It is not evidence that dreams genuinely
14:01
Speaker 2: provide information about events that have not yet happened. The
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Speaker 2: distinction matters because powerful experiences can feel convincing without being
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Speaker 2: reliable sources of information about the outside world. Ancient Greece
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Speaker 2: developed an equally rich relationship with dreams. Dreams could be
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Speaker 2: associated with divine communication, prophecy and healing. People seeking relief
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Speaker 2: from illness sometimes visited sanctuaries associated with Asclepius, the Greek
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Speaker 2: god of medicine. At some of these healing centres, visitors
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Speaker 2: slept in the hope of receiving a significant dream that
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Speaker 2: might offer guidance or be interpreted in relation to their condition.
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Speaker 2: Yet Greek thought also contains an important shift towards more
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Speaker 2: natural explanations. Aristotle considered dreams without treating every one of
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Speaker 2: them as a supernatural message. He explored the possibility that
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Speaker 2: dream experiences emerged from perception, memory and bodily processes continuing
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Speaker 2: during sleep. This may sound fairly modest now, but it
15:03
Speaker 2: represents a profound change in the question being asked. Instead
15:08
Speaker 2: of assuming that a dream had been sent into the mind,
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Speaker 2: one could ask whether the mind itself was producing it.
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Speaker 2: That shift would eventually become central to the scientific study
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Speaker 2: of dreaming. Ideas about dreams as journeys or communications were
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Speaker 2: never limited to one region of the ancient world. Across
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Speaker 2: different societies dreams have been interpreted as encounters with ancestors,
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Speaker 2: visits from dead relatives, glimpses of events yet to happen,
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Speaker 2: or experiences undertaken by some non-physical aspect of the person
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Speaker 2: while the body remained asleep. The details vary enormously between cultures,
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Speaker 2: which is important in itself. Human beings do not merely dream.
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Speaker 2: We interpret dreams through whatever ideas about reality, death, spirits, gods,
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Speaker 2: and the mind are available to us. And dreams almost
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Speaker 2: invite extraordinary explanations. Imagine living in a world without any
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Speaker 2: scientific account of sleep and dreaming, that you have spent
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Speaker 2: an hour speaking with somebody who died many years earlier.
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Speaker 2: They look like themselves. They speak in their familiar voice.
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Speaker 2: Perhaps they tell you something. During the dream, there may
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Speaker 2: be no sensation of pretending or imagining. The meeting can
16:23
Speaker 2: feel immediate and real. Then you wake to discover that
16:27
Speaker 2: you never left the bed. Without a model of a
16:30
Speaker 2: brain capable of constructing convincing people, voices and environments internally,
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Speaker 2: the idea that the encounter occurred somewhere beyond ordinary waking
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Speaker 2: reality would be deeply tempting. Even today, knowing that dreams
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Speaker 2: are generated by sleeping brains does not necessarily make them
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Speaker 2: feel less meaningful. A dream about someone we miss can
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Speaker 2: affect our mood for the entire day. A frightening dream
16:56
Speaker 2: can leave the heart racing after the imagined danger has vanished.
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Speaker 2: An absurd dream can somehow acquire a sense of importance
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Speaker 2: that survives long after its details stop making sense. This
17:09
Speaker 2: reveals something important about the human mind. We are exceptionally
17:13
Speaker 2: good at constructing narratives. When several strange images appear together,
17:18
Speaker 2: the waking mind tends to look for connections. If an
17:21
Speaker 2: old friend... a storm and a childhood home all appear
17:25
Speaker 2: in the same dream, it is very easy to assume
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Speaker 2: that there must be some hidden reason joining them together.
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Speaker 2: Sometimes there may be meaningful connections. Dreams can draw upon memories,
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Speaker 2: concerns and emotional experiences from waking life. But meaningful interpretation
17:42
Speaker 2: and deliberate construction are not the same thing. A dream
17:45
Speaker 2: does not need to have been carefully designed in order
17:48
Speaker 2: for the dreamer to discover meaning within it afterwards. That
17:52
Speaker 2: difference gradually became increasingly important as the study of the
17:56
Speaker 2: mind moved towards psychology, physiology and eventually neuroscience. The central
18:03
Speaker 2: question changed. Instead of asking which god, spirit or external
18:08
Speaker 2: force had placed an image into the sleeping mind, researchers
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Speaker 2: began asking what the sleeping brain was doing when the
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Speaker 2: image appeared. That change did not make dreams less strange.
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Speaker 2: It simply moved the source of the mystery. The impossible
18:22
Speaker 2: landscape was no longer somewhere the sleeper had travelled. The
18:25
Speaker 2: voice of the absent person no longer required someone outside
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Speaker 2: the dream to be speaking. The sleeping brain itself had
18:32
Speaker 2: somehow built the place, supplied the characters, produced the conversation
18:37
Speaker 2: and created the temporary certainty that all of it was
18:40
Speaker 2: really happening. And once dreams were understood in that way,
18:45
Speaker 2: an ancient question about messages from somewhere else became a
18:49
Speaker 2: scientific question. about one of the most inventive things the
18:52
Speaker 2: human brain does entirely on its own. Sleep can feel
18:56
Speaker 2: like one long disappearance. You close your eyes, several hours vanish,
19:01
Speaker 2: and then morning arrives. From the inside, particularly on nights
19:05
Speaker 2: when no dreams are remembered, the whole thing can seem
19:08
Speaker 2: almost featureless. But the sleeping brain is anything but featureless.
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Speaker 2: Throughout the night, it moves through a repeating sequence of
19:17
Speaker 2: recognisably different states. each with its own patterns of electrical activity,
19:22
Speaker 2: eye movement, muscle tone and responsiveness to the outside world.
19:27
Speaker 2: Sleep is not one condition maintained continuously until morning. It
19:32
Speaker 2: has an architecture. The broadest division separates rapid eye movement
19:37
Speaker 2: sleep from non-rapid eye movement sleep. Non-rapid eye movement sleep
19:41
Speaker 2: is itself divided into several stages, beginning with the light
19:45
Speaker 2: transition away from wakefulness. and eventually reaching the deepest form
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Speaker 2: of ordinary sleep. The first stage is the doorway. As
19:54
Speaker 2: wakefulness gives way to sleep, awareness of the room begins
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Speaker 2: to loosen. Thoughts can become fragmented. Sounds from outside may
20:03
Speaker 2: still be noticed, but attention towards them becomes less reliable.
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Speaker 2: A person awakened during this period may occasionally insist that
20:11
Speaker 2: they had not actually fallen asleep at all. Electrical recordings
20:15
Speaker 2: of the brain show the organised rhythms of relaxed wakefulness
20:18
Speaker 2: beginning to change, activity becomes less dominated by the patterns
20:23
Speaker 2: associated with an alert waking brain, and slower frequencies become
20:28
Speaker 2: more prominent. This first stage is normally brief. The sleeper
20:33
Speaker 2: then moves into the second stage of non-rapid eye movement sleep.
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Speaker 2: which occupies a surprisingly large proportion of an ordinary night's sleep. Here,
20:43
Speaker 2: the brain produces several distinctive electrical events. One is the
20:47
Speaker 2: sleep spindle. A sleep spindle is a brief burst of
20:50
Speaker 2: rhythmic brain activity, usually lasting roughly a fraction of a
20:54
Speaker 2: second to a few seconds. These events arise through interactions
20:59
Speaker 2: involving the thalamus and the cerebral cortex, and they appear
21:03
Speaker 2: repeatedly throughout this stage. Researchers have connected sleep spindles with
21:07
Speaker 2: processes including sensory filtering and memory, although their exact functions
21:12
Speaker 2: are still being investigated. Another characteristic event is a large
21:17
Speaker 2: isolated electrical pattern known as the K-complex. These events can
21:21
Speaker 2: occur spontaneously or in response to something in the environment,
21:25
Speaker 2: such as a sound. Rather than showing that the sleeping
21:29
Speaker 2: brain has switched off, they help demonstrate almost the opposite.
21:33
Speaker 2: The brain continues to monitor and regulate its relationship with
21:37
Speaker 2: the outside world, even while conscious awareness of that world
21:40
Speaker 2: has been greatly reduced. The third stage is deep non-rapid
21:45
Speaker 2: eye movement sleep, often called slow wave sleep. Here, large
21:50
Speaker 2: populations of neurons repeatedly shift between more active and less
21:54
Speaker 2: active states in a coordinated way. On electrical recordings, this
21:58
Speaker 2: produces the large slow waves that give the stage its name.
22:03
Speaker 2: These waves are among the clearest signs that deep sleep
22:06
Speaker 2: is an organised biological condition, rather than simply an absence
22:10
Speaker 2: of wakefulness. Waking someone from deep, slow-wave sleep can be difficult,
22:15
Speaker 2: and when awakening does occur, the person may feel confused
22:19
Speaker 2: or disoriented for a short time. Deep sleep is also
22:22
Speaker 2: associated with several important restorative processes throughout the body and brain.
22:28
Speaker 2: Hormone release, metabolic regulation, immune activity and memory processing, all
22:33
Speaker 2: interact with sleep, although it would be misleading to assign
22:37
Speaker 2: every benefit to one particular stage. After passing through these
22:41
Speaker 2: deeper forms of non-rapid eye movement sleep, the brain eventually
22:45
Speaker 2: changes direction. It moves towards rapid eye movement sleep. This
22:51
Speaker 2: stage looks peculiar almost everywhere researchers measure it. The eyes
22:55
Speaker 2: begin producing bursts of rapid movement beneath the closed eyelids,
23:00
Speaker 2: brain activity becomes more active, and, in some respects, resembles
23:04
Speaker 2: patterns found during wakefulness. Heart rate and breathing can become
23:09
Speaker 2: more variable. Autonomic activity shifts. Yet while the brain becomes
23:14
Speaker 2: remarkably active, most of the body's skeletal muscles become profoundly relaxed.
23:20
Speaker 2: This reduction in muscle activity is known as muscle atonia.
23:24
Speaker 2: During rapid eye movement sleep, brainstem systems suppress much of
23:28
Speaker 2: the motor output that would otherwise reach the major muscles
23:31
Speaker 2: of the body. The eyes remain capable of moving, breathing continues,
23:37
Speaker 2: and small twitches may occur, but the large muscles involved
23:40
Speaker 2: in ordinary movement are mostly prevented from acting out whatever
23:44
Speaker 2: the brain may be experiencing. It is a useful arrangement.
23:49
Speaker 2: Running from something in a dream is far less troublesome
23:52
Speaker 2: when the legs stay in bed. These stages do not
23:55
Speaker 2: occur once and then disappear. They repeat. An adult typically
24:00
Speaker 2: progresses through several sleep cycles over the course of a night,
24:04
Speaker 2: moving through combinations of non-rapid eye movement sleep and rapid
24:08
Speaker 2: eye movement sleep again and again. A commonly quoted figure
24:12
Speaker 2: places a complete cycle at around an hour and a half.
24:15
Speaker 2: That is useful as a rough guide, but it should
24:18
Speaker 2: not be treated as a 90-minute metronome ticking beside the bed.
24:22
Speaker 2: Individual cycles vary in length. Different people show different patterns.
24:28
Speaker 2: and even within one person, one cycle may not last
24:31
Speaker 2: exactly as long as the next. The composition of the
24:34
Speaker 2: cycles changes as the night continues as well. Earlier in
24:38
Speaker 2: the night, deep slow-wave sleep is generally more prominent. As
24:42
Speaker 2: morning approaches, deep sleep becomes less dominant, and periods of
24:46
Speaker 2: rapid eye movement sleep tend to grow longer. This changing
24:50
Speaker 2: structure helps explain something familiar about dream recall. If an
24:55
Speaker 2: alarm wakes someone late in the night, there is a
24:58
Speaker 2: reasonable chance that the awakening will interrupt a relatively long
25:02
Speaker 2: period of rapid eye movement sleep. Because vivid and elaborate
25:06
Speaker 2: dreams are especially common during this state, the dream may
25:10
Speaker 2: still be present in memory as the person wakes. The
25:14
Speaker 2: result can be that unmistakable feeling of having been dropped
25:17
Speaker 2: abruptly from one world into another. Wake earlier from deep
25:22
Speaker 2: non-rapid eye movement sleep and the experience may be quite different.
25:27
Speaker 2: But rapid eye movement sleep does not own dreaming. People
25:31
Speaker 2: awakened from non-rapid eye movement sleep also report experiences. On average,
25:36
Speaker 2: reports collected after rapid eye movement awakenings tend to be
25:40
Speaker 2: more vivid, visual, emotional and narratively elaborate. They are more
25:44
Speaker 2: likely to resemble the complicated dreams people usually mean when
25:48
Speaker 2: they say they had a dream. Reports from non-rapid eye
25:52
Speaker 2: movement sleep are often shorter, less visually intense and more thought-like.
25:57
Speaker 2: But these are tendencies, not rigid boundaries. A rich dream
26:02
Speaker 2: can occur outside rapid eye movement sleep, while an awakening
26:06
Speaker 2: from rapid eye movement sleep does not guarantee an elaborate
26:09
Speaker 2: remembered story. Researchers learned much of this by studying sleeping
26:14
Speaker 2: volunteers in laboratories using polysomnography. Polysomnography combines several measurements at
26:21
Speaker 2: the same time. Electrical activity from the brain can be
26:25
Speaker 2: recorded through electrodes placed on the scalp. Eye movements can
26:29
Speaker 2: be measured using electrodes positioned near the eyes. Muscle activity,
26:34
Speaker 2: often recorded from the chin, helps reveal the dramatic reduction
26:37
Speaker 2: in muscle tone associated with rapid eye movement sleep. Breathing,
26:42
Speaker 2: heart rhythm, blood oxygen levels and other physiological signals can
26:46
Speaker 2: also be monitored when required. Together, these measurements allow researchers
26:51
Speaker 2: to identify which sleep stage a person is in with
26:54
Speaker 2: remarkable precision. They can then wake the sleeper, and ask
26:58
Speaker 2: a wonderfully simple question. What was going through your mind
27:03
Speaker 2: just before you woke? By comparing those reports with the
27:06
Speaker 2: physiological state immediately beforehand, scientists can begin connecting private experience
27:13
Speaker 2: with measurable brain activity. And what emerges is a picture
27:17
Speaker 2: of sleep that is far more active than its outward
27:20
Speaker 2: appearance suggests. From across the room, a sleeping person may
27:24
Speaker 2: seem to be doing almost nothing. Inside the nervous system, however,
27:30
Speaker 2: rhythms are changing, networks are communicating, memories are being processed,
27:35
Speaker 2: sensory information is being filtered, muscles are being actively restrained,
27:40
Speaker 2: and conscious experience may appear, disappear, and change character several
27:45
Speaker 2: times before morning. The night is not a blank interval
27:49
Speaker 2: between two waking days. It is a carefully structured journey
27:52
Speaker 2: through several different biological states. And somewhere within that shifting architecture,
27:57
Speaker 2: again and again, the sleeping brain begins to dream. For
28:01
Speaker 2: a very long time, dreams could be discussed, interpreted and remembered.
28:05
Speaker 2: But they were difficult to measure. A person could wake
28:08
Speaker 2: from a vivid dream and describe it in great detail.
28:11
Speaker 2: They might report a conversation, a landscape, a frightening chase
28:16
Speaker 2: or an impossible journey. But from the outside, there was
28:20
Speaker 2: no obvious sign showing exactly when that experience had occurred.
28:25
Speaker 2: The sleeper simply looked to sleep. That changed dramatically in
28:29
Speaker 2: the early 1950s at the University of Chicago. A young
28:33
Speaker 2: researcher named Eugene Aserinsky was working with the physiologist Nathaniel Claytman,
28:39
Speaker 2: one of the major figures in the emerging scientific study
28:42
Speaker 2: of sleep. At the time, sleep was still often treated
28:46
Speaker 2: as a relatively passive condition, almost as though the brain
28:50
Speaker 2: simply turned down its activity until morning. Aserinsky began recording
28:54
Speaker 2: the movements of sleeping people's eyes using electrodes placed near them.
28:59
Speaker 2: What he noticed was unusual. At certain points during the night,
29:03
Speaker 2: the eyes beneath the closed eyelids began moving rapidly from
29:06
Speaker 2: side to side. These were not occasional random flickers. The
29:10
Speaker 2: movements appeared in distinctive bursts. More importantly, they returned repeatedly
29:16
Speaker 2: during the night. That regularity suggested that something organised was happening.
29:22
Speaker 2: Aserinsky and Kleitman investigated further, combining measurements of eye movements
29:27
Speaker 2: with recordings of brain activity. Their results, published in 1953,
29:32
Speaker 2: described recurring periods of rapid eye movement during sleep and
29:36
Speaker 2: showed that these episodes were associated with a distinctive physiological state.
29:41
Speaker 2: Then came the observation that would change dream research. When
29:45
Speaker 2: sleeping volunteers were awakened during these rapid eye movement periods,
29:50
Speaker 2: they frequently reported that they had been dreaming, not merely
29:53
Speaker 2: vague thoughts or a faint sense that something had been happening,
29:57
Speaker 2: but often vivid, elaborate experiences. When awakenings occurred outside those periods,
30:04
Speaker 2: reports of dreams were generally less frequent. For the first time,
30:08
Speaker 2: researchers had something remarkably valuable. They had a measurable physiological
30:13
Speaker 2: pattern that was strongly associated with dream reports. Dreaming had
30:17
Speaker 2: not suddenly become directly observable. The private experience itself was
30:22
Speaker 2: still available only to the dreamer, but scientists now had
30:26
Speaker 2: a way of predicting when a person was particularly likely
30:29
Speaker 2: to report having been in the middle of a dream.
30:33
Speaker 2: That was an enormous advance. Instead of simply asking someone
30:37
Speaker 2: the following morning whether they remembered dreaming at some point
30:40
Speaker 2: during the night, researchers could watch the sleeping body, identify
30:44
Speaker 2: a particular physiological state, wake the person immediately and ask
30:49
Speaker 2: what had been happening in their mind seconds earlier. Dream
30:53
Speaker 2: science had gained a clock. William Dement, who later became
30:57
Speaker 2: one of the best-known sleep researchers of the 20th century,
31:01
Speaker 2: worked with Nathaniel Kleitman to study these patterns in greater detail.
31:06
Speaker 2: Their research helped reveal the repeating organisation of sleep across
31:10
Speaker 2: the night. Rapid eye movement sleep was not a single
31:13
Speaker 2: event appearing once before morning. It alternated with non-rapid eye
31:18
Speaker 2: movement sleep in recurring cycles. these cycles changed as the
31:23
Speaker 2: night progressed. Rapid eye movement periods were generally shorter earlier
31:27
Speaker 2: in the night and became longer towards morning, while deep,
31:31
Speaker 2: slow-wave sleep was concentrated more heavily in the earlier hours.
31:36
Speaker 2: The apparently simple act of sleeping was beginning to look
31:39
Speaker 2: like a carefully organised sequence of changing brain states, and
31:42
Speaker 2: because vivid dream reports were so strongly associated with rapid
31:46
Speaker 2: eye movement awakenings, it was tempting to reach a very
31:49
Speaker 2: simple conclusion. Perhaps rapid eye movement sleep was dreaming. For
31:54
Speaker 2: a time, the two became so closely linked that popular
31:57
Speaker 2: descriptions often treated them almost as the same thing. But
32:02
Speaker 2: later research complicated that picture. People awakened from non-rapid eye
32:07
Speaker 2: movement sleep can also report conscious experiences. Sometimes those reports
32:12
Speaker 2: are short and relatively thought-like. A person may say they
32:16
Speaker 2: were thinking about a problem, remembering a conversation, or experiencing
32:20
Speaker 2: a vague scene. But non-rapid eye movement dreams can also
32:24
Speaker 2: be vivid, emotional and elaborate. At the same time, waking
32:29
Speaker 2: someone during rapid eye movement sleep does not guarantee that
32:32
Speaker 2: they will produce a rich cinematic account. The relationship is strong,
32:37
Speaker 2: but it is not absolute. On average, rapid eye movement
32:40
Speaker 2: dream reports tend to be more visual, more emotional and
32:44
Speaker 2: more narratively complex. They are often populated by characters, changing
32:50
Speaker 2: locations and events that unfold, with the peculiar logic familiar
32:54
Speaker 2: from memorable dreams. Experiences reported from non-rapid eye movement sleep
33:00
Speaker 2: are more variable, but the boundaries overlap. This distinction turned
33:05
Speaker 2: out to be important, because it prevented researchers from replacing
33:09
Speaker 2: one mystery with an oversimplification. Rapid eye movement sleep is
33:13
Speaker 2: a physiological state. Dreaming is a subjective experience. They are
33:19
Speaker 2: closely connected, but they are not identical. The rapid eye
33:24
Speaker 2: movements themselves produced another intriguing question. What exactly are the
33:29
Speaker 2: eyes doing? A tempting image is that the dreamer is
33:33
Speaker 2: somehow watching the dream as though an internal film were
33:36
Speaker 2: being projected behind the eyelids, with the eyes moving around
33:40
Speaker 2: to follow the action. That is probably too simple. Dreams
33:44
Speaker 2: do not appear to be literal films being displayed somewhere
33:47
Speaker 2: inside the skull. However, Some experiments have found relationships between
33:52
Speaker 2: eye movements and changes in dream imagery or shifts of
33:56
Speaker 2: attention within dream scenes. In certain studies, especially those involving
34:02
Speaker 2: lucid dreamers who can deliberately signal with their eyes while
34:06
Speaker 2: remaining asleep, eye movements have provided researchers with a remarkable
34:11
Speaker 2: bridge between the dreamer's private experience and the laboratory outside.
34:16
Speaker 2: Even so, the movements should not be imagined as nothing
34:20
Speaker 2: more than eyes tracking an internal screen. Rapid eye movement
34:25
Speaker 2: sleep involves widespread changes throughout the brain and body. The
34:29
Speaker 2: eyes are simply one of its most visible signatures, and
34:33
Speaker 2: that visibility helped transform an entire field. Before the 1950s,
34:40
Speaker 2: dreams were often studied mainly through interpretation. A dream would
34:43
Speaker 2: be remembered, described, and then analysed for possible meaning. After
34:49
Speaker 2: the discovery of rapid eye movement sleep, researchers could begin
34:54
Speaker 2: asking a different kind of question. What is the brain
34:57
Speaker 2: doing while dreams occur? They could compare electrical activity between
35:01
Speaker 2: different sleep states. They could measure muscle tone. They could
35:05
Speaker 2: observe breathing, heart activity and eye movements. They could wake
35:10
Speaker 2: people at carefully selected moments rather than waiting for morning.
35:14
Speaker 2: The dream report could now be placed beside a physiological record.
35:19
Speaker 2: That did not solve the mystery of dreaming. In some ways,
35:22
Speaker 2: it made the mystery more precise. Scientists could increasingly identify
35:27
Speaker 2: the biological conditions associated with particular kinds of dream experience.
35:33
Speaker 2: They could describe when rapid eye movement sleep appeared, how
35:36
Speaker 2: long it lasted, how the brain behaved during it, and
35:40
Speaker 2: how often vivid dreams were reported after awakening from it.
35:45
Speaker 2: But one question remained stubbornly separate. Why should any of
35:49
Speaker 2: that activity feel like something from the inside? Why should
35:53
Speaker 2: a particular arrangement of sleeping neural activity become a street,
35:57
Speaker 2: a face, a conversation, or the sensation of falling through
36:01
Speaker 2: the sky? The discovery of rapid eye movement sleep gave
36:06
Speaker 2: scientists an extraordinary new way to study dreaming. It turned
36:10
Speaker 2: the sleeping eye into a measurable clue. but the eyes
36:14
Speaker 2: themselves were never the dream. They were simply the sign
36:17
Speaker 2: that something remarkable was happening behind them. During a vivid dream,
36:23
Speaker 2: the body can appear to be doing almost anything. You
36:26
Speaker 2: might be sprinting down a street, climbing a mountain, swimming
36:30
Speaker 2: through deep water, throwing a punch, or making a heroic
36:34
Speaker 2: leap across a gap that would look considerably less sensible
36:37
Speaker 2: in daylight. Inside the dream, the movements can feel completely convincing.
36:43
Speaker 2: Outside the dream, however, very little may be happening. The
36:47
Speaker 2: sleeper is still lying in bed. One of the strangest
36:52
Speaker 2: features of rapid eye movement sleep is a dramatic reduction
36:56
Speaker 2: in the activity of most of the skeletal muscles that
36:58
Speaker 2: normally allow us to move around the world. This condition
37:02
Speaker 2: is known as rapid eye movement sleepatonia. Muscle tone does
37:07
Speaker 2: not disappear everywhere, and the word paralysis can be slightly
37:11
Speaker 2: misleading if taken too literally. But compared with ordinary wakefulness,
37:16
Speaker 2: the major muscles of the body become remarkably inactive. The
37:20
Speaker 2: reason lies partly within the brainstem. During rapid eye movement sleep,
37:25
Speaker 2: networks within the lower parts of the brain become involved
37:28
Speaker 2: in suppressing motor activity. Signals passing down towards the spinal
37:33
Speaker 2: cord activate inhibitory mechanisms that make many motor neurons much
37:37
Speaker 2: less likely to produce strong muscular contractions. The motor system
37:41
Speaker 2: has not vanished. it has been restrained. That distinction matters
37:46
Speaker 2: because the sleeping brain can still generate remarkably detailed representations
37:52
Speaker 2: of movement. Motor regions can remain active while a person
37:57
Speaker 2: dreams about running or reaching for something. The dreamer may
38:00
Speaker 2: experience the unmistakable sensation of moving through an environment, but
38:05
Speaker 2: much of the command that would normally turn that experience
38:08
Speaker 2: into large physical movements is prevented from reaching the muscles
38:11
Speaker 2: with its usual effect. The result is a curious separation.
38:16
Speaker 2: The brain can rehearse movement while the body stays largely still.
38:20
Speaker 2: It would be incorrect, however, to imagine that the entire
38:23
Speaker 2: body becomes completely paralysed. The eyes are an obvious exception.
38:28
Speaker 2: They continue making the rapid movements that give this stage
38:32
Speaker 2: of sleep its name. The muscles responsible for breathing must
38:36
Speaker 2: also keep working. The diaphragm continues contracting rhythmically so that
38:40
Speaker 2: air can move in and out of the lungs. Small
38:43
Speaker 2: movements can occur as well. A finger may twitch, a
38:47
Speaker 2: facial muscle may briefly contract, a foot may move slightly.
38:52
Speaker 2: Anyone who has watched a sleeping dog apparently attempting a
38:55
Speaker 2: very modest run while lying on its side will recognise
38:59
Speaker 2: the general idea. So rapid eye movement sleepotonia is better
39:03
Speaker 2: understood as a powerful suppression of most ordinary skeletal movement
39:07
Speaker 2: rather than a perfect shutdown of every muscle. The advantage
39:11
Speaker 2: seems immediately obvious. Dreams are not known for respecting practical limitations.
39:17
Speaker 2: If every movement represented inside a dream were converted directly
39:21
Speaker 2: into full-strength physical action, sleeping would become considerably more complicated.
39:27
Speaker 2: Someone dreaming of running could attempt to sprint into a wall.
39:31
Speaker 2: Someone dreaming of fighting might strike a bedside table. Someone
39:35
Speaker 2: dreaming of jumping could discover rather abruptly that mattresses do
39:39
Speaker 2: not extend very far in the vertical direction. By reducing
39:43
Speaker 2: most skeletal movement, Rapid eye movement sleep allows the brain
39:47
Speaker 2: to generate elaborate simulations of action without requiring the body
39:51
Speaker 2: to perform them. The importance of this system becomes especially
39:56
Speaker 2: clear when it stops working properly. Rapid eye movement sleep
40:00
Speaker 2: behaviour disorder is a condition in which the normal suppression
40:04
Speaker 2: of movement during rapid eye movement sleep is reduced or absent.
40:08
Speaker 2: People with the disorder may physically enact parts of their dreams,
40:12
Speaker 2: Movements can include talking, shouting, reaching, kicking, punching or suddenly
40:17
Speaker 2: sitting up. Some episodes are relatively mild. Others can become
40:21
Speaker 2: forceful enough to injure the sleeper or someone sharing the bed.
40:26
Speaker 2: Researchers can identify the condition during sleep studies because muscle
40:30
Speaker 2: recordings show unusually persistent activity during periods when rapid eye
40:34
Speaker 2: movement sleep would normally produce marked atoniae. Rapid eye movement
40:39
Speaker 2: sleep behaviour disorder is not the same as ordinary sleep
40:42
Speaker 2: talking or the small twitches many healthy people experience. It
40:47
Speaker 2: is also distinct from several other parasomnias. Parasomnias are unusual
40:51
Speaker 2: behaviours or experiences occurring during sleep, while falling asleep or
40:56
Speaker 2: while waking. Sleepwalking, for example, typically emerges from deep, non-rapid
41:02
Speaker 2: eye movement sleep rather than from ordinary rapid eye movement dreaming.
41:06
Speaker 2: A person can therefore perform complicated movements during sleep without
41:10
Speaker 2: those movements necessarily representing a dream being acted out in
41:15
Speaker 2: the way seen in rapid eye movement sleep behaviour disorder.
41:20
Speaker 2: There is another experience that reveals the same machinery from
41:23
Speaker 2: almost the opposite direction. Sleep paralysis occurs when conscious awareness
41:28
Speaker 2: returns before rapid eye movement related muscle atonia has fully ended.
41:34
Speaker 2: A person may wake and realise that they are in bed.
41:37
Speaker 2: They can see the room. They may hear ordinary sounds.
41:41
Speaker 2: But for several seconds, and occasionally longer, they find themselves
41:46
Speaker 2: unable to move normally. The experience can be extremely unsettling.
41:50
Speaker 2: It becomes stranger because dreamlike imagery can sometimes overlap with
41:54
Speaker 2: waking awareness. People may report sensing a presence in the room,
41:59
Speaker 2: seeing a figure, hearing a voice, feeling pressure on the chest.
42:04
Speaker 2: or experiencing the impression that someone or something is nearby. Historically,
42:09
Speaker 2: experiences like these helped inspire supernatural explanations involving spirits, demons,
42:16
Speaker 2: or night visitors. Modern sleep science provides a rather different interpretation.
42:22
Speaker 2: Part of the brain has returned to waking awareness, while
42:25
Speaker 2: elements of rapid eye movement physiology and dream imagery have
42:30
Speaker 2: not yet completely disappeared. The room is real. The inability
42:34
Speaker 2: to move is real. The threatening figure may be generated
42:38
Speaker 2: by the brain. For a few moments, waking consciousness and
42:42
Speaker 2: dreaming physiology overlap. Together, these phenomena reveal something unusual about
42:48
Speaker 2: rapid eye movement sleep. The brain can generate a world
42:52
Speaker 2: filled with movement while simultaneously restricting the body's ability to
42:56
Speaker 2: participate in it. You can dream of running without running.
43:00
Speaker 2: You can dream of shouting while remaining silent. You can
43:04
Speaker 2: experience falling while lying perfectly flat. And if the system
43:08
Speaker 2: is briefly mistimed, consciousness may return before the body has
43:13
Speaker 2: been released from its sleeping restraint. Dreaming is therefore not
43:18
Speaker 2: simply ordinary wakefulness made dimmer. It is a distinctive physiological condition.
43:24
Speaker 2: Perception is largely generated internally. Movement can be vividly represented
43:29
Speaker 2: while physical action is suppressed. The brain becomes capable of
43:34
Speaker 2: constructing places, bodies and events that feel immediate, while the
43:39
Speaker 2: real body remains mostly disconnected from those imagined demands. For
43:43
Speaker 2: several minutes at a time, the mind can be elsewhere,
43:47
Speaker 2: and the body, quite sensibly, stays behind. A vivid dream
43:51
Speaker 2: can be convincing enough to fool the person having it.
43:55
Speaker 2: You may stand in a house that could not possibly exist,
43:58
Speaker 2: speak with someone who is not really there, or watch
44:01
Speaker 2: the sky change colour while accepting the entire situation without
44:05
Speaker 2: much objection. The experience may contain movement, emotion, faces, voices,
44:12
Speaker 2: and a strong sense of location. For a while, it
44:15
Speaker 2: does not feel like an image being deliberately invented inside
44:18
Speaker 2: the head. It feels like being somewhere. That raises an
44:22
Speaker 2: obvious question. What is the brain actually doing while all
44:26
Speaker 2: of this is happening? The first thing to avoid is
44:29
Speaker 2: the old image of the sleeping brain as a machine
44:32
Speaker 2: that has simply been switched off for the night. Sleep
44:35
Speaker 2: is an active biological state, and the pattern of activity
44:39
Speaker 2: depends strongly on which stage of sleep a person is
44:41
Speaker 2: passing through. Even within a particular stage, activity is not
44:46
Speaker 2: evenly distributed. Some systems become quieter, some remain busy, and
44:52
Speaker 2: others behave in ways that differ substantially from ordinary waking life.
44:57
Speaker 2: Rapid eye movement sleep provides one of the clearest examples.
45:01
Speaker 2: Brain imaging studies have shown that during this state many
45:04
Speaker 2: regions can be remarkably active. Areas involved in processing visual information,
45:10
Speaker 2: emotion and memory may show substantial activity even while the
45:14
Speaker 2: person lies with closed eyes and receives very little useful
45:18
Speaker 2: visual information from the outside world. That begins to explain
45:22
Speaker 2: how a sleeping brain can produce something that feels so rich.
45:26
Speaker 2: consider vision. When you're awake, light enters the eyes and
45:30
Speaker 2: is converted into neural signals by the retina. Those signals
45:34
Speaker 2: travel through the brain and are progressively processed by several
45:37
Speaker 2: visual regions. During a dream, the eyes may be closed
45:41
Speaker 2: in a dark room. There may be no mountain, no face,
45:44
Speaker 2: no corridor, and no bright blue sea in front of
45:47
Speaker 2: the sleeper. Yet visual association areas can still become active.
45:52
Speaker 2: These regions normally help the brain interpret and organise visual information.
45:57
Speaker 2: They contribute to recognising objects, faces, spaces, movement and other
46:03
Speaker 2: features that make a visual world intelligible. During dreaming, activity
46:08
Speaker 2: within visual networks can help generate imagery from the inside,
46:12
Speaker 2: rather than simply analysing light arriving from outside. The brain
46:17
Speaker 2: does not need an actual red car in front of
46:20
Speaker 2: the eyes to produce an experience containing a red car.
46:24
Speaker 2: It already possesses neural systems capable of representing colour, shape,
46:29
Speaker 2: movement and objects. Dreaming gives those systems an unusual opportunity
46:34
Speaker 2: to build without the normal requirement that the construction agree
46:38
Speaker 2: closely with incoming sensory evidence. Emotion can become equally powerful.
46:44
Speaker 2: One structure frequently discussed in relation to emotional processing is
46:48
Speaker 2: the amygdala. The amygdala consists of groups of neurons deep
46:52
Speaker 2: within the temporal lobes and participates in several processes involving
46:56
Speaker 2: emotional significance, learning and responses to important events, particularly events
47:03
Speaker 2: related to threat or reward. Brain imaging has found substantial
47:08
Speaker 2: activity in the amygdala and other limbic and paralimbic regions
47:11
Speaker 2: during rapid eye movement sleep. That does not mean the
47:15
Speaker 2: amygdala is a simple fear button. Its role is much
47:18
Speaker 2: broader than that. But increased engagement of emotional networks offers
47:23
Speaker 2: one plausible reason dreams can possess such extraordinary emotional intensity.
47:29
Speaker 2: A minor inconvenience in a dream can feel catastrophic. An
47:33
Speaker 2: ordinary conversation may carry enormous importance. A vague figure at
47:37
Speaker 2: the end of a corridor can produce a level of
47:39
Speaker 2: fear that would seem rather excessive if encountered as a
47:43
Speaker 2: coat hanging from a door the following morning. The emotion
47:47
Speaker 2: is not pretend emotion. Even though the event generating it
47:51
Speaker 2: is internally produced, the emotional experience can be genuine. At
47:55
Speaker 2: the same time, other parts of the brain behave differently
47:58
Speaker 2: from the waking state. Researchers have frequently observed reduced activity
48:03
Speaker 2: in portions of the prefrontal cortex during ordinary rapid eye
48:07
Speaker 2: movement dreaming, particularly regions of the dorsolateral prefrontal cortex. associated
48:13
Speaker 2: with executive functions such as working memory, planning, cognitive control
48:18
Speaker 2: and some forms of self-monitoring. This is sometimes simplified into
48:23
Speaker 2: the claim that the logical part of the brain switches
48:25
Speaker 2: off during dreams. That is much too crude. The prefrontal
48:30
Speaker 2: cortex is not a single logic department, and dreamers are
48:33
Speaker 2: not completely incapable of reasoning. People can solve problems in dreams,
48:38
Speaker 2: make plans and respond coherently to events. The difference appears
48:43
Speaker 2: to involve changes in the balance of systems supporting executive
48:46
Speaker 2: monitoring and metacognition. Metacognition is the ability to monitor and
48:51
Speaker 2: reflect upon one's own mental processes. When it is reduced,
48:56
Speaker 2: bizarre events may be accepted with surprisingly little resistance. You
49:01
Speaker 2: can enter your childhood home and discover that it is
49:03
Speaker 2: somehow inside an airport. A teacher from school can become
49:07
Speaker 2: your neighbour halfway through a conversation. You may travel from
49:11
Speaker 2: London to the moon by walking through a kitchen door,
49:14
Speaker 2: and instead of stopping to say that several laws of
49:17
Speaker 2: reality appear to have become optional, the dreaming mind often
49:21
Speaker 2: continues with the story. The experience feels normal from within,
49:25
Speaker 2: because the systems that would usually inspect contradictions and compare
49:29
Speaker 2: them with a stable model of reality are operating differently.
49:33
Speaker 2: Memory contributes another layer. The hippocampus and neighbouring medial temporal
49:38
Speaker 2: structures are deeply involved in memory, especially in forming and
49:42
Speaker 2: organising memories of events and relationships. Sleep itself is closely
49:47
Speaker 2: connected with memory processing. But dreaming does not normally replay
49:51
Speaker 2: waking memories like recordings stored on a shelf. Instead, fragments
49:56
Speaker 2: can be extracted and recombined. A dream house may have
50:00
Speaker 2: the hallway of a childhood home, the kitchen of a
50:03
Speaker 2: recent hotel and a garden that never existed. A person
50:07
Speaker 2: may have the face of one friend, but somehow be
50:10
Speaker 2: understood to be someone else. A conversation from yesterday may
50:15
Speaker 2: appear in a location not visited for 20 years. This
50:19
Speaker 2: peculiar mixture makes sense if dreaming draws upon distributed memory
50:23
Speaker 2: systems rather than simply opening complete stored scenes. Memories are
50:28
Speaker 2: not perfect films. They are reconstructed patterns of information. And
50:33
Speaker 2: when the sleeping brain works with them, reconstruction can become
50:37
Speaker 2: unusually inventive. This also helps explain why dreams often feel
50:41
Speaker 2: both familiar and novel at the same time. The ingredients
50:45
Speaker 2: may be recognisable. The arrangement is new. Researchers have also
50:49
Speaker 2: examined the behaviour of a large-scale network spanning many parts
50:53
Speaker 2: of the brain. One of these is called the default
50:56
Speaker 2: mode network. It includes regions that tend to be active
50:59
Speaker 2: during internally directed mental activity, including autobiographical memory, imagining situations.
51:07
Speaker 2: thinking about oneself and considering other people's minds. Elements of
51:11
Speaker 2: this network appear relevant to the internally generated nature of dreaming.
51:16
Speaker 2: Other networks involved in sensory processing, emotion and attention contribute
51:21
Speaker 2: as well. But there is no single dream centre hidden
51:25
Speaker 2: somewhere in the brain. No tiny region turns on and
51:29
Speaker 2: projects the dream. Dreaming appears to emerge from the coordinated
51:33
Speaker 2: and changing activity of many interacting systems. Different networks contribute imagery, memory, emotion,
51:41
Speaker 2: bodily sensation, movement and the sense of self. The exact
51:45
Speaker 2: balance also changes between dreams and between stages of sleep.
51:50
Speaker 2: This complexity is one reason researchers have become cautious about
51:54
Speaker 2: assigning any single brain region a simple role such as
51:57
Speaker 2: creating dreams or generating consciousness. Brain imaging can reveal which
52:02
Speaker 2: regions become more active or less active under particular conditions.
52:07
Speaker 2: Researchers can compare those patterns with reports collected after awakening.
52:12
Speaker 2: They can sometimes identify neural activity associated with certain features
52:16
Speaker 2: of an experience. What brain imaging cannot yet do is
52:20
Speaker 2: explain the deepest part of the transformation. A scanner might
52:24
Speaker 2: reveal activity in visual areas while someone dreams of a face.
52:29
Speaker 2: It may reveal emotional networks becoming active during a frightening dream.
52:33
Speaker 2: It may show altered communication between regions while the sleeper
52:37
Speaker 2: accepts an impossible event. Those are important correlations. But the
52:41
Speaker 2: measurements themselves do not tell us why electrical and chemical
52:45
Speaker 2: activity should become the felt experience of seeing that face,
52:49
Speaker 2: fearing that danger or standing inside that impossible room. That
52:54
Speaker 2: is part of the larger problem of consciousness. The sleeping
52:57
Speaker 2: brain makes the problem especially vivid because so little is
53:01
Speaker 2: coming from the outside world. A person can lie motionless
53:05
Speaker 2: in darkness while neural activity creates colour, distance, voices, memories,
53:11
Speaker 2: movement and emotion. The brain does not merely display random flashes.
53:16
Speaker 2: It can assemble them into an experienced world. And for
53:20
Speaker 2: a while, that world can be convincing enough that the
53:23
Speaker 2: person inside it never thinks to ask where it came from.
53:27
Speaker 2: One of the strangest things about dreaming is not that
53:30
Speaker 2: impossible events happen. It is that they often seem perfectly
53:34
Speaker 2: reasonable while they are happening. You may discover that you
53:37
Speaker 2: can fly and simply continue with your evening. You may
53:41
Speaker 2: walk into your kitchen and find someone who died many
53:44
Speaker 2: years ago sitting at the table without immediately wondering how
53:48
Speaker 2: this rather significant development has occurred. You may return to
53:52
Speaker 2: a school you left decades earlier and accept that you
53:55
Speaker 2: apparently have an exam in ten minutes. A room can
53:59
Speaker 2: become a railway station halfway through a conversation. A person
54:03
Speaker 2: can change identity without changing appearance. An entire afternoon can
54:08
Speaker 2: apparently pass between two sentences. And through all of this,
54:12
Speaker 2: the dreaming mind may raise remarkably few objections. If exactly
54:18
Speaker 2: the same events happened while awake, the reaction would be
54:21
Speaker 2: rather different. Part of the explanation comes from what the
54:25
Speaker 2: sleeping brain is receiving from the outside world. During ordinary
54:29
Speaker 2: waking life, Perception is continually constrained by incoming information. Light
54:35
Speaker 2: reaches the eyes. Sound reaches the ears. The body provides
54:40
Speaker 2: information about balance, position, temperature and touch. If you believe
54:44
Speaker 2: you're standing in a kitchen but your eyes, ears and
54:47
Speaker 2: body all provide evidence that you're actually sitting on a bus,
54:51
Speaker 2: reality has a fairly strong vote in the matter. During sleep,
54:56
Speaker 2: that external competition is greatly reduced. The eyes are usually closed.
55:01
Speaker 2: The body is largely still. Sounds from the environment may
55:05
Speaker 2: continue to reach the nervous system, but much of that
55:08
Speaker 2: information is filtered or fails to enter conscious awareness. Internally
55:13
Speaker 2: generated activity therefore has an unusual amount of freedom. If
55:18
Speaker 2: the sleeping brain constructs a street, there may be very
55:21
Speaker 2: little sensory evidence available to contradict the street. If it
55:25
Speaker 2: produces the face of an old friend, No competing image
55:29
Speaker 2: from the actual bedroom needs to replace it. The internally
55:32
Speaker 2: generated world can temporarily become the world that consciousness inhabits.
55:38
Speaker 2: That alone does not explain why absurdities go unnoticed. Another
55:42
Speaker 2: part involves metacognition. Metacognition is the ability to monitor one's
55:48
Speaker 2: own thinking and experience. It includes recognising that a thought
55:52
Speaker 2: is strange, noticing a contradiction, questioning an assumption. or asking
55:58
Speaker 2: whether something makes sense. During ordinary dreaming, this kind of
56:03
Speaker 2: reflective monitoring appears to be reduced. The brain can still reason.
56:08
Speaker 2: Dreamers can make decisions, solve immediate problems, and respond sensibly
56:13
Speaker 2: within the situation they believe themselves to occupy. But they
56:18
Speaker 2: are often much less likely to stand back mentally and
56:21
Speaker 2: inspect the situation itself. The question is not necessarily whether
56:27
Speaker 2: you can work out how to escape from the building.
56:30
Speaker 2: You may do that perfectly well. The missing question is
56:34
Speaker 2: why the building has suddenly appeared in the middle of
56:36
Speaker 2: the ocean. This reduced reflective awareness fits with changes seen
56:42
Speaker 2: in parts of the prefrontal cortex during ordinary rapid eye
56:46
Speaker 2: movement dreaming. Regions associated with executive control, working memory and
56:52
Speaker 2: self-monitoring often behave differently from the waking state. It would
56:57
Speaker 2: be too simple to say that logic switches off. Dreams
57:00
Speaker 2: can contain plenty of logical thought. What changes is the
57:04
Speaker 2: degree to which the mind checks its own model of reality.
57:08
Speaker 2: This allows remarkably large discontinuities to pass without inspection. Dream
57:13
Speaker 2: geography is especially flexible. You may begin in your childhood bedroom,
57:18
Speaker 2: walk through the door and arrive in an office you
57:20
Speaker 2: worked in years later. Nothing feels like teleportation. The transition
57:25
Speaker 2: simply happens. Time behaves similarly. A dream can seem to
57:30
Speaker 2: contain long periods while actually occurring during a much shorter
57:34
Speaker 2: interval of sleep. At other times, scenes jump abruptly forward
57:40
Speaker 2: without the dreamer noticing that anything is missing. Identity can
57:44
Speaker 2: be just as unstable. A dream character may begin as
57:48
Speaker 2: a friend, somehow become a sibling, and then be understood
57:52
Speaker 2: as a complete stranger while retaining the same face. Yet
57:56
Speaker 2: dreams usually preserve enough local coherence for the experience to
58:00
Speaker 2: feel continuous. One event leads into another. There is still
58:05
Speaker 2: a sense of being somewhere. There is still a temporary
58:08
Speaker 2: present moment. The story may not survive careful inspection, but
58:13
Speaker 2: from one moment to the next it often hangs together
58:16
Speaker 2: just well enough. This becomes particularly interesting when compared with
58:21
Speaker 2: waking perception. Even while awake, the brain does not simply
58:25
Speaker 2: receive a perfect copy of the external world. Sensory information
58:29
Speaker 2: is incomplete. The nervous system continually interprets it, using context,
58:35
Speaker 2: previous experience and expectations. Your visual system fills in missing information.
58:41
Speaker 2: It maintains the impression of a stable world despite constant
58:45
Speaker 2: eye movements. It makes rapid assumptions about objects from partial
58:49
Speaker 2: views and uses previous knowledge to interpret ambiguous scenes. Some
58:54
Speaker 2: modern theories describe perception partly in terms of prediction. In
58:59
Speaker 2: broad predictive processing accounts, the brain generates expectations about the
59:04
Speaker 2: causes of sensory information and continually updates those expectations when
59:09
Speaker 2: incoming expectations evidence disagrees with them. The important point is
59:14
Speaker 2: not that waking life is secretly a dream. It is not.
59:18
Speaker 2: Waking perception is tightly constrained by sensory information originating outside
59:23
Speaker 2: the brain. If your internal prediction says there is a
59:27
Speaker 2: doorway ahead, but your eyes show a brick wall The
59:30
Speaker 2: wall tends to win. Dreaming changes that balance. External sensory
59:36
Speaker 2: evidence becomes weaker, while internally generated activity becomes comparatively dominant.
59:43
Speaker 2: A dream can therefore be thought of, cautiously, as an
59:46
Speaker 2: extreme case in which perception is being constructed with much
59:51
Speaker 2: less correction from the outside world. The brain is still
59:55
Speaker 2: building an experienced reality. It is simply working with a
59:59
Speaker 2: very different supply of evidence. Emotion may help that reality
1:00:03
Speaker 2: feel convincing. Logical plausibility is not always the most important
1:00:08
Speaker 2: thing inside a dream. Emotional plausibility can be much stronger.
1:00:13
Speaker 2: If you are terrified, the danger feels real. If you
1:00:17
Speaker 2: are embarrassed, the social disaster seems important. If you meet
1:00:21
Speaker 2: someone you love... The affection can feel immediate even when
1:00:25
Speaker 2: the circumstances make absolutely no sense. The emotional reaction itself
1:00:31
Speaker 2: is genuine brain activity. Your fear does not become imaginary
1:00:35
Speaker 2: merely because the monster producing it does not exist. That
1:00:39
Speaker 2: intensity can help hold the dream together. A scene may
1:00:42
Speaker 2: be logically impossible but emotionally coherent. You are being chased,
1:00:48
Speaker 2: so you run. You have lost something important, so you search.
1:00:53
Speaker 2: You've returned to school and somehow forgotten to revise, so
1:00:57
Speaker 2: the familiar anxiety provides enough structure that nobody stops to
1:01:01
Speaker 2: ask why a person who left school 30 years ago
1:01:04
Speaker 2: is suddenly worried about double mathematics. Then waking arrives. External
1:01:11
Speaker 2: sensory information floods back in. The bedroom reappears. Executive monitoring strengthens.
1:01:18
Speaker 2: Working memory becomes more stable. and within moments the entire
1:01:22
Speaker 2: construction is judged by waking standards. This is when the
1:01:26
Speaker 2: problems become obvious. Of course the school was wrong. Of
1:01:30
Speaker 2: course that person could not have been there. Of course
1:01:33
Speaker 2: rooms do not change into airports. Of course human beings
1:01:37
Speaker 2: cannot usually fly simply by leaning forward and developing confidence.
1:01:41
Speaker 2: The remarkable thing is how quickly certainty can reverse. Seconds earlier,
1:01:46
Speaker 2: the dream world may have been accepted as reality. Now
1:01:50
Speaker 2: it can seem ridiculous. That contrast reveals how strongly the
1:01:54
Speaker 2: feeling of reality depends on the state of the brain
1:01:57
Speaker 2: doing the judging. Dreaming does not require the sleeping mind
1:02:01
Speaker 2: to lose every ability to reason. It only requires a
1:02:04
Speaker 2: different balance between internally generated experience, external sensory evidence, memory,
1:02:11
Speaker 2: emotion and self-monitoring. With the bedroom largely excluded, emotional systems active,
1:02:19
Speaker 2: memories recombined and reality-checking reduced, an impossible world can become
1:02:24
Speaker 2: temporarily convincing. Not because the dream is secretly obeying hidden rules,
1:02:31
Speaker 2: but because for a while the brain has stopped demanding
1:02:34
Speaker 2: that the world inside it obey the rules outside. There
1:02:39
Speaker 2: is a particular kind of frustration that belongs almost entirely
1:02:42
Speaker 2: to dreaming. You wake with the dream still there. For
1:02:46
Speaker 2: a few seconds it may seem complete. You know where
1:02:50
Speaker 2: you were. You remember who was with you. There was
1:02:53
Speaker 2: a conversation, perhaps a problem, perhaps an entire sequence of
1:02:57
Speaker 2: events that felt as though it had been unfolding for ages.
1:03:02
Speaker 2: Then something begins to slip. A face becomes harder to picture.
1:03:07
Speaker 2: The location loses its shape. You remember that something important happened,
1:03:12
Speaker 2: but not what it was. Within a minute or two,
1:03:15
Speaker 2: the dream that felt so vivid while it was happening
1:03:18
Speaker 2: may be reduced to a handful of disconnected fragments, and
1:03:22
Speaker 2: sometimes even those disappear before you have properly opened your eyes.
1:03:26
Speaker 2: The easiest mistake is to assume that a forgotten dream
1:03:29
Speaker 2: must have been weak or insignificant in the first place,
1:03:33
Speaker 2: but experiencing something and successfully storing it as a durable
1:03:37
Speaker 2: memory are not the same process. A dream can be rich, emotional,
1:03:43
Speaker 2: and convincing while it is happening without leaving behind a
1:03:46
Speaker 2: strong memory that survives into the waking day. Ordinary waking
1:03:51
Speaker 2: memory depends on several stages, and experience has to be
1:03:55
Speaker 2: attended to, encoded, stabilized, and later retrieved. Not everything that
1:04:02
Speaker 2: enters consciousness completes that journey. Even during the day, entire conversations, journeys,
1:04:08
Speaker 2: and routine activities can vanish from memory because they were
1:04:12
Speaker 2: never encoded strongly enough to remain accessible. Dreams have an
1:04:16
Speaker 2: additional difficulty. They occur inside a brain whose chemistry and
1:04:20
Speaker 2: patterns of activity differ substantially from those of ordinary wakefulness.
1:04:25
Speaker 2: During rapid eye movement sleep, several neurotransmitter systems operate differently.
1:04:31
Speaker 2: One particularly interesting example is norepinephrine. Norepinephrine is involved in arousal,
1:04:38
Speaker 2: attention and aspects of memory formation during waking life. Neurons
1:04:42
Speaker 2: in a brainstem region called the locus coeruleus provide much
1:04:47
Speaker 2: of the brain's norepinephrine and their activity becomes very low
1:04:51
Speaker 2: during rapid eye movement sleep. Other chemical systems change as well. Acetylcholine,
1:04:57
Speaker 2: for example, remains relatively active during rapid eye movement sleep.
1:05:01
Speaker 2: while serotonin and norepinephrine activity fall dramatically compared with waking levels.
1:05:07
Speaker 2: This unusual chemical environment may contribute to the strange mixture
1:05:11
Speaker 2: of vivid experience and poor later recall that characterises many dreams.
1:05:17
Speaker 2: It would be too simple to say that low norepinephrine
1:05:20
Speaker 2: is the reason dreams are forgotten. Memory during sleep involves
1:05:24
Speaker 2: many interacting brain systems, and dream forgetting almost certainly cannot
1:05:28
Speaker 2: be reduced to one chemical. But the neurochemical conditions of
1:05:32
Speaker 2: rapid eye movement sleep are different from those in which
1:05:35
Speaker 2: waking memories are usually formed, and that difference appears to matter.
1:05:40
Speaker 2: Another important factor is what happens immediately after the dream.
1:05:44
Speaker 2: Suppose a dream ends and the sleeper moves smoothly into
1:05:47
Speaker 2: another stage of sleep. There may be no moment of
1:05:50
Speaker 2: waking attention. No effort is made to rehearse the experience.
1:05:54
Speaker 2: No sentence is formed describing what just happened. The dream
1:05:59
Speaker 2: is simply followed by more sleep. Under those conditions, even
1:06:03
Speaker 2: a vivid experience may leave very little accessible trace by morning.
1:06:07
Speaker 2: Waking changes the situation. If a person wakes directly from
1:06:11
Speaker 2: a dream, particularly from rapid eye movement sleep, the experience
1:06:15
Speaker 2: has a better chance of being remembered because it can
1:06:18
Speaker 2: immediately be attended to. This is one reason alarms often
1:06:22
Speaker 2: seem to catch people in the middle of dreams. The
1:06:25
Speaker 2: alarm may interrupt the experience before it has had time
1:06:27
Speaker 2: to fade into another sleep stage. Spontaneous awakenings can do
1:06:32
Speaker 2: the same thing. An especially emotional dream may also be
1:06:36
Speaker 2: easier to remember, partly because emotional intensity can strengthen attention
1:06:40
Speaker 2: and memory. A nightmare that ends with the heart racing
1:06:43
Speaker 2: is therefore more likely to survive the transition into wakefulness
1:06:47
Speaker 2: than a quiet dream about wandering through an unfamiliar supermarket. Although, naturally,
1:06:54
Speaker 2: the supermarket dream may have contained a profound crisis involving
1:06:57
Speaker 2: the missing bread aisle. People also differ enormously in how
1:07:01
Speaker 2: often they remember dreams. Some report dreams almost every morning.
1:07:06
Speaker 2: Others may remember one every few weeks, or even less often.
1:07:09
Speaker 2: That does not necessarily mean the frequent dreamer is dreaming
1:07:12
Speaker 2: much more. Dream recall and dream production are different things.
1:07:16
Speaker 2: A person who rarely remembers dreams may still be experiencing
1:07:20
Speaker 2: them regularly but failing to wake at the right moments
1:07:22
Speaker 2: or failing to preserve them long enough for later recall.
1:07:26
Speaker 2: Researchers have found individual differences in factors such as sleep patterns, awakenings,
1:07:32
Speaker 2: attention towards dreams and brain activity associated with responsiveness to
1:07:37
Speaker 2: internal and external events. Interest also matters. Someone who routinely
1:07:42
Speaker 2: pays attention to dreams is more likely to remember them
1:07:45
Speaker 2: than someone who wakes and immediately begins thinking about the
1:07:49
Speaker 2: day ahead. This is why keeping a dream diary can
1:07:52
Speaker 2: make dream recall noticeably better. The effect does not require
1:07:55
Speaker 2: anything mystical. If you wake and remain still for a moment,
1:08:00
Speaker 2: deliberately reconstruct the dream and then write it down, you
1:08:03
Speaker 2: are rehearsing the memory. Attention strengthens it. Putting the experience
1:08:08
Speaker 2: into words provides additional structure. Repeating this habit also trains
1:08:12
Speaker 2: the waking mind to treat dream material as something worth
1:08:15
Speaker 2: retaining rather than something disposable. After several mornings, details that
1:08:20
Speaker 2: previously vanished may begin to survive. This does not necessarily
1:08:24
Speaker 2: mean the person has started dreaming more. They may simply
1:08:28
Speaker 2: have become better at catching dreams before they disappear. Forgetting
1:08:32
Speaker 2: the content of a dream also does not prove that
1:08:34
Speaker 2: nothing happened in the brain, simply because the experience cannot
1:08:38
Speaker 2: later be reported. Memory processing continues during sleep. Emotional and
1:08:44
Speaker 2: cognitive systems remain active. A dream that cannot be consciously
1:08:48
Speaker 2: recalled the next morning may have occurred perfectly normally. At
1:08:51
Speaker 2: the same time, it would be equally unjustified to claim
1:08:54
Speaker 2: that every forgotten dream must secretly influence later behaviour. The
1:08:59
Speaker 2: fact that an experience has been forgotten does not automatically
1:09:03
Speaker 2: make it psychologically powerful. Sometimes, forgotten information influences later processing. Sometimes,
1:09:11
Speaker 2: it simply disappears from accessible memory. The evidence has to
1:09:14
Speaker 2: be examined rather than assumed. This creates a fundamental problem
1:09:19
Speaker 2: for dream science. Researchers usually learn about a dream only
1:09:23
Speaker 2: after it is over. They can measure brain activity continuously.
1:09:27
Speaker 2: They can record eye movements and muscle tone. They can
1:09:29
Speaker 2: wake a sleeper at carefully chosen moments. But the content
1:09:33
Speaker 2: of the dream still has to be reported from memory.
1:09:36
Speaker 2: And memory is imperfect. A person may forget parts of
1:09:40
Speaker 2: the dream before speaking. They may unintentionally reorganise events while
1:09:44
Speaker 2: describing them, a vague image can become more definite once
1:09:48
Speaker 2: language is applied to it. The scientific record of a
1:09:52
Speaker 2: dream is therefore never exactly the dream itself. It is
1:09:55
Speaker 2: a reconstruction made immediately afterwards. That limitation does not make
1:10:01
Speaker 2: dream research impossible. It simply means that researchers have to
1:10:05
Speaker 2: remain careful about what dream reports can and cannot reveal.
1:10:09
Speaker 2: Perhaps that is also why dreams feel so fragile in
1:10:11
Speaker 2: the morning. For a few minutes, The brain has been
1:10:15
Speaker 2: producing an entire experienced world. Then waking consciousness returns under
1:10:20
Speaker 2: different conditions, with different priorities, different chemistry and an external
1:10:25
Speaker 2: world demanding attention. The dream has only a brief opportunity
1:10:29
Speaker 2: to cross that boundary. If it is noticed, rehearsed and remembered,
1:10:34
Speaker 2: it may remain for years. If not, a whole night
1:10:37
Speaker 2: of impossible places and borrowed faces can disappear before breakfast.
1:10:41
Speaker 2: leaving behind little more than the peculiar certainty that something
1:10:45
Speaker 2: happened while you were away. By the end of the
1:10:48
Speaker 2: 19th century, dreams had travelled a long way from temples,
1:10:51
Speaker 2: omens and messages from the gods. They had not, however,
1:10:54
Speaker 2: become ordinary. For Sigmund Freud, dreams were not meaningless fragments
1:10:59
Speaker 2: produced by a sleeping brain. They were psychologically important events,
1:11:05
Speaker 2: and he believed that examining them could reveal mental processes
1:11:08
Speaker 2: normally hidden from conscious awareness. His most famous work on
1:11:12
Speaker 2: the subject was The Interpretation of Dreams. The book was
1:11:16
Speaker 2: technically published in 1899, although the publisher dated it 1900.
1:11:22
Speaker 2: That small publishing curiosity is why 1900 is usually given
1:11:25
Speaker 2: as the conventional date. Freud placed dreaming near the centre
1:11:29
Speaker 2: of the psychoanalytic system he was developing. His starting point
1:11:33
Speaker 2: was that the human mind contained wishes, memories, impulses and conflicts.
1:11:39
Speaker 2: that were not always available to conscious awareness. Some thoughts,
1:11:43
Speaker 2: he argued, were actively repressed because they were uncomfortable, unacceptable
1:11:47
Speaker 2: or difficult to reconcile with a person's conscious view of themselves.
1:11:51
Speaker 2: Dreaming offered those hidden processes an opportunity to appear. But
1:11:56
Speaker 2: according to Freud, they rarely appear directly. He distinguished between
1:12:01
Speaker 2: what he called the manifest content of a dream and
1:12:04
Speaker 2: its latent content. The manifest content was the dream as
1:12:08
Speaker 2: the person remembered it. Perhaps you are standing in an
1:12:11
Speaker 2: old house. Perhaps a door will not open. Perhaps you
1:12:14
Speaker 2: miss a train, lose your shoes, meet somebody from childhood
1:12:18
Speaker 2: and then somehow find yourself walking along a beach. That
1:12:23
Speaker 2: sequence of remembered events would be the manifest content. The
1:12:27
Speaker 2: latent content, in Freud's theory, was something deeper. It was
1:12:31
Speaker 2: the collection of unconscious wishes, conflicts and thoughts, that supposedly
1:12:36
Speaker 2: lay behind the dream and had been transformed into the
1:12:39
Speaker 2: strange images appearing during sleep. The dream, in other words,
1:12:43
Speaker 2: was not necessarily saying what it seemed to be saying.
1:12:47
Speaker 2: Freud believed that a process sometimes translated as dream work
1:12:52
Speaker 2: transformed latent material into the manifest dream. Different thoughts could
1:12:57
Speaker 2: be condensed into a single person or object. Emotional importance
1:13:02
Speaker 2: could be displaced from one thing onto another. Ideas could
1:13:05
Speaker 2: be represented through imagery rather than direct statements. By the
1:13:11
Speaker 2: time the dream reached consciousness, its original psychological meaning might
1:13:15
Speaker 2: therefore be disguised. One of Freud's most famous claims was
1:13:19
Speaker 2: that dreams represented forms of wish fulfilment. That phrase can
1:13:24
Speaker 2: easily be misunderstood. He did not simply mean that every
1:13:27
Speaker 2: dream gives the dreamer something pleasant. Clearly dreams can be frightening,
1:13:31
Speaker 2: humiliating and miserable. Freud's proposal was that beneath the surface,
1:13:37
Speaker 2: dreams could provide indirect expression for wishes or impulses that
1:13:40
Speaker 2: could not comfortably appear in conscious thought in an obvious form.
1:13:44
Speaker 2: The remembered dream might therefore look nothing like a straightforward wish.
1:13:49
Speaker 2: It had supposedly been transformed, disguised and rearranged. This gave
1:13:54
Speaker 2: dream interpretation an unusual quality. An apparently innocent image could
1:13:58
Speaker 2: be treated as standing for something entirely different. The task
1:14:03
Speaker 2: of the psychoanalyst was to work backwards from the remembered
1:14:07
Speaker 2: dream towards the hidden thoughts believed to have produced it.
1:14:10
Speaker 2: These ideas became enormously influential. Freud's work helped establish the
1:14:15
Speaker 2: expectation that dreams were psychologically meaningful and deserved serious attention.
1:14:21
Speaker 2: His influence spread far beyond clinical psychology. Books, films, novels
1:14:27
Speaker 2: and everyday conversation absorbed the idea that dreams were coded
1:14:30
Speaker 2: messages from the unconscious. Even people who have never read
1:14:34
Speaker 2: Freud may still respond to a strange dream by assuming
1:14:38
Speaker 2: that it must secretly mean something. A dream about a
1:14:41
Speaker 2: lift probably represents something. A dream about losing your teeth
1:14:45
Speaker 2: must have a hidden message. A dream in which you
1:14:48
Speaker 2: arrive at work wearing no trousers surely cannot just be
1:14:50
Speaker 2: the sleeping brain having an unusually inconvenient evening. That expectation
1:14:55
Speaker 2: owes a great deal to the intellectual world Freud helped create.
1:14:59
Speaker 2: Historical influence, however, is not the same thing as scientific confirmation.
1:15:04
Speaker 2: Modern experimental dream research does not generally accept Freud's specific
1:15:09
Speaker 2: theory of disguised wish fulfilment as an established explanation for
1:15:13
Speaker 2: why humans dream. One major problem is testing it. A
1:15:18
Speaker 2: strong scientific theory should make predictions that could, at least
1:15:22
Speaker 2: in principle, turn out to be wrong. Freudian dream interpretations
1:15:27
Speaker 2: can be difficult to test in this way. because almost
1:15:30
Speaker 2: any dream can potentially be reinterpreted after the fact. If
1:15:34
Speaker 2: a dream seems to express a wish directly, that may
1:15:37
Speaker 2: support the theory. If it appears to express the opposite
1:15:41
Speaker 2: of a wish, the theory can sometimes accommodate that by
1:15:44
Speaker 2: suggesting that the wish has been disguised. If the dream
1:15:49
Speaker 2: contains something unrelated, that too can potentially be treated as symbolic.
1:15:54
Speaker 2: When an explanation can stretch to fit almost every possible outcome,
1:15:59
Speaker 2: Demonstrating that it is specifically correct becomes much harder. That
1:16:04
Speaker 2: does not mean dreams are unrelated to waking life. Quite
1:16:08
Speaker 2: the opposite. Modern research repeatedly finds that dream content often
1:16:12
Speaker 2: incorporates people, concerns, emotions, memories and events connected with waking experience.
1:16:19
Speaker 2: The important difference is that this does not require a
1:16:22
Speaker 2: universal hidden code. Psychologist Calvin Hall played an important role
1:16:27
Speaker 2: in moving dream research towards systematic analysis of what people
1:16:31
Speaker 2: actually reported dreaming about. Rather than treating each dream primarily
1:16:36
Speaker 2: as a puzzle containing disguised symbols, Hall and later researchers
1:16:40
Speaker 2: examined recurring patterns across large collections of dream reports. This
1:16:45
Speaker 2: work helped support approaches often grouped around the continuity hypothesis.
1:16:50
Speaker 2: The basic idea is fairly intuitive. Dreams frequently continue themes
1:16:54
Speaker 2: that matter during waking life. Someone worrying about work may
1:16:58
Speaker 2: dream about work. A student thinking about an examination may
1:17:02
Speaker 2: dream about being unprepared. A person missing somebody may dream
1:17:06
Speaker 2: about seeing them again. Relationships, fears, routines and recent experiences
1:17:11
Speaker 2: can all find their way into dreams, but continuity does
1:17:14
Speaker 2: not mean perfect replay. Dreams distort. They combine recent experiences
1:17:19
Speaker 2: with older memories. They place familiar people in unfamiliar settings.
1:17:24
Speaker 2: They can exaggerate worries, mix several concerns together, or produce
1:17:28
Speaker 2: scenes whose connection with waking life is obvious only in
1:17:32
Speaker 2: a very broad sense. This is a much less rigid
1:17:35
Speaker 2: claim than saying that a particular object always has one
1:17:38
Speaker 2: particular meaning. Consider the familiar dream of teeth falling out.
1:17:43
Speaker 2: There is no scientifically established dictionary stating that this experience
1:17:47
Speaker 2: must represent one hidden fear shared by everyone who dreams it.
1:17:51
Speaker 2: For one person, it might occur during a period of
1:17:54
Speaker 2: concern about appearance. For another, it could follow an actual
1:17:59
Speaker 2: visit to the dentist. For someone else, it may have
1:18:02
Speaker 2: no obvious waking connection at all. The same applies to
1:18:06
Speaker 2: being naked in public. It might accompany feelings of embarrassment
1:18:09
Speaker 2: or vulnerability, or it might simply be a bizarre dream.
1:18:14
Speaker 2: Missing an examination is another common theme. For someone still studying,
1:18:18
Speaker 2: the connection may be fairly obvious. For somebody who left
1:18:21
Speaker 2: school 30 years earlier, the dream may draw on an
1:18:24
Speaker 2: old emotional pattern of being judged, being late, or feeling unprepared.
1:18:30
Speaker 2: But there is no need to assume that every examination
1:18:32
Speaker 2: dream contains precisely the same message. Context matters. Individual lives matter.
1:18:39
Speaker 2: And sometimes a dream may be memorable without having any
1:18:42
Speaker 2: profound hidden significance whatsoever. Freud's contribution therefore occupies an unusual position.
1:18:50
Speaker 2: His detailed theory of disguised wish fulfilment has not become
1:18:53
Speaker 2: the accepted scientific explanation of dreaming. Modern neuroscience approaches the
1:18:58
Speaker 2: subject through sleep stages, brain activity, memory, emotion, and experimentally
1:19:04
Speaker 2: testable processes, rather than relying on symbolic interpretation alone. Yet
1:19:09
Speaker 2: Freud profoundly changed how people thought about dreams. He insisted
1:19:14
Speaker 2: that the strange experiences of sleep deserved psychological attention. He
1:19:18
Speaker 2: helped make dreams central to discussions about memory, desire and
1:19:22
Speaker 2: the unconscious. And he left behind one of the most
1:19:25
Speaker 2: persistent ideas in popular psychology, that when the sleeping mind
1:19:30
Speaker 2: produces something strange, there must be another story underneath it.
1:19:34
Speaker 2: Modern science is rather more cautious. Dreams clearly borrow from
1:19:38
Speaker 2: our lives. They can contain our worries, our relationships and
1:19:42
Speaker 2: our memories. But whether every strange image is hiding a
1:19:46
Speaker 2: coded message is another matter entirely. For much of the
1:19:50
Speaker 2: 20th century, one of the most influential ways of thinking
1:19:53
Speaker 2: about dreams came from the idea that they contained hidden
1:19:56
Speaker 2: psychological meanings. Then, in the 1970s, two psychiatrists offered a
1:20:02
Speaker 2: very different possibility. John Alan Hobson and Robert Macaulay were
1:20:06
Speaker 2: studying the physiology of sleep when they proposed what became
1:20:10
Speaker 2: known as the activation synthesis hypothesis. Instead of beginning with
1:20:14
Speaker 2: the question of what a dream symbolised, they began with
1:20:17
Speaker 2: the machinery of the sleeping brain. Their proposal was published
1:20:21
Speaker 2: in 1977 and focused particularly on rapid eye movement sleep,
1:20:25
Speaker 2: when the brain enters a highly active physiological state, even
1:20:29
Speaker 2: though the sleeper remains largely disconnected from the outside world.
1:20:33
Speaker 2: Hobson and Macaulay argued that activity generated within the sleeping
1:20:37
Speaker 2: brain could provide the raw material from which dreams were constructed.
1:20:41
Speaker 2: Signals arising from lower brain regions, particularly within the brainstem,
1:20:46
Speaker 2: could activate areas involved in perception, emotion and memory. Higher
1:20:51
Speaker 2: regions of the brain would then attempt to organise that
1:20:53
Speaker 2: activity into something resembling a coherent experience. In simplified form,
1:21:00
Speaker 2: The idea became famous as the brain making a story
1:21:02
Speaker 2: out of random noise. That phrase is useful, but it
1:21:06
Speaker 2: needs some care. The neural activity involved in rapid eye
1:21:09
Speaker 2: movement sleep is not necessarily random in the strict mathematical sense.
1:21:14
Speaker 2: The sleeping brain remains an organised biological system. Different regions
1:21:18
Speaker 2: communicate in structured ways. Particular neurotransmitter systems change their activity.
1:21:24
Speaker 2: Repeating physiological patterns appear during rapid eye movement sleep. So
1:21:29
Speaker 2: the proposal was not really that the brain receives meaningless
1:21:32
Speaker 2: electrical static like a badly tuned radio. The important idea
1:21:36
Speaker 2: was that much of the activity driving the dream could
1:21:39
Speaker 2: arise internally, rather than being caused by events happening in
1:21:42
Speaker 2: the outside world. Once that internal activity reaches higher brain systems,
1:21:48
Speaker 2: the brain does something it is remarkably good at doing.
1:21:51
Speaker 2: It tries to make sense of it. Imagine a fragment
1:21:54
Speaker 2: of activity associated with a familiar face. Another pattern may
1:21:59
Speaker 2: activate something connected with movement. An emotional system may contribute anxiety.
1:22:05
Speaker 2: A memory network may supply a railway station visited years ago.
1:22:09
Speaker 2: The sleeping brain does not necessarily experience these as four
1:22:13
Speaker 2: unrelated pieces of neural activity. It can combine them. Now
1:22:18
Speaker 2: you are standing on the railway platform. The familiar person
1:22:21
Speaker 2: is there. Something urgent is happening. A train is leaving.
1:22:26
Speaker 2: You do not know exactly why you need to catch it,
1:22:29
Speaker 2: but within the dream the situation already seems to possess
1:22:31
Speaker 2: a history. The brain has constructed a scene. Memory provides
1:22:36
Speaker 2: an enormous supply of material for this process. Dreams frequently
1:22:41
Speaker 2: contain places, people and situations with some connection to waking life,
1:22:45
Speaker 2: but those ingredients do not have to be retrieved faithfully.
1:22:49
Speaker 2: A childhood home can appear on the wrong street. A
1:22:52
Speaker 2: person seen yesterday can be placed beside someone not encountered
1:22:55
Speaker 2: for 20 years. A recent worry can become attached to
1:22:59
Speaker 2: a completely unrelated setting. Emotional associations may help determine which
1:23:04
Speaker 2: memories are recruited, while visual systems provide the imagery needed
1:23:08
Speaker 2: to turn fragments into an experienced environment. This helps explain
1:23:13
Speaker 2: one of the most characteristic features of dreaming. The story
1:23:17
Speaker 2: often seems to be assembled while it's happening. A dream
1:23:20
Speaker 2: may begin in one location and suddenly continue somewhere else.
1:23:25
Speaker 2: A conversation can change subject without any transition. A person
1:23:29
Speaker 2: can disappear and another take their place. Yet the dream
1:23:32
Speaker 2: rarely pauses to announce that the plot has developed a
1:23:36
Speaker 2: fairly serious continuity problem. Instead, the mind tends to accommodate
1:23:40
Speaker 2: the latest event. If the railway station has suddenly become
1:23:44
Speaker 2: a hotel, then apparently the railway station was always a hotel.
1:23:48
Speaker 2: The story adjusts. This is one reason activation synthesis was
1:23:52
Speaker 2: so attractive as an explanation for the discontinuities of dreams.
1:23:57
Speaker 2: If internally generated activity is constantly providing new material, the
1:24:02
Speaker 2: brain may repeatedly build interpretations around whatever appears. The narrative
1:24:07
Speaker 2: does not necessarily have to exist in complete form before
1:24:10
Speaker 2: the dream begins. It can be constructed moment by moment.
1:24:14
Speaker 2: Hobson's thinking continued to develop long after the original activation
1:24:19
Speaker 2: synthesis proposal. He increasingly emphasised that dreaming should be understood
1:24:23
Speaker 2: as a form of consciousness produced when the brain occupies
1:24:26
Speaker 2: a distinctive physiological state. Changes in brain activation, the source
1:24:32
Speaker 2: of information reaching conscious systems and the chemical environment in
1:24:35
Speaker 2: which neurons operate can all alter the character of experience.
1:24:39
Speaker 2: In waking life, consciousness is heavily constrained by sensory information
1:24:44
Speaker 2: arriving from the external world. During dreaming, that balance changes.
1:24:49
Speaker 2: Internally generated information becomes far more important. Hobson later developed
1:24:55
Speaker 2: broader models describing differences between waking, dreaming and other conscious
1:25:00
Speaker 2: states through changes in brain activation, information input and neuromodulation.
1:25:06
Speaker 2: He also explored the possibility that dreaming reflects something fundamental
1:25:11
Speaker 2: about how the brain constructs conscious experience rather than merely
1:25:15
Speaker 2: producing occasional meaningless stories during sleep. But activation synthesis created
1:25:21
Speaker 2: an important distinction that remains useful even if the original
1:25:26
Speaker 2: theory is not accepted in every detail. There's a difference
1:25:30
Speaker 2: between explaining how a dream is produced and explaining why
1:25:34
Speaker 2: dreaming exists. Suppose activation within the sleeping brain generates visual images.
1:25:41
Speaker 2: Suppose memory systems contribute familiar people and places. Suppose emotional
1:25:47
Speaker 2: networks influence the mood. Suppose higher brain regions organise these
1:25:52
Speaker 2: ingredients into a narrative. That would provide part of a
1:25:55
Speaker 2: mechanism for creating dreams. It would not necessarily tell us
1:26:00
Speaker 2: whether dreaming has a biological purpose. This is the difference
1:26:04
Speaker 2: between mechanism and function. Mechanism asks how something happens. Function
1:26:10
Speaker 2: asks what useful role, if any, the process evolved to perform.
1:26:16
Speaker 2: The distinction is easy to overlook. The heart pumps blood,
1:26:20
Speaker 2: and pumping blood clearly serves a biological function. But not
1:26:25
Speaker 2: every consequence of an active biological system must itself be
1:26:29
Speaker 2: an adaptation. Some phenomena emerge because other useful processes are
1:26:34
Speaker 2: taking place. Dreaming could conceivably be important in its own right,
1:26:39
Speaker 2: or dream experience could partly be a consequence of neural
1:26:42
Speaker 2: processes that are performing other tasks during sleep. Activation synthesis
1:26:48
Speaker 2: alone does not settle that argument. There is also good
1:26:51
Speaker 2: reason not to describe dream content as meaningless static. Dreams
1:26:56
Speaker 2: are often systematically connected with waking life. Recent experiences appear
1:27:02
Speaker 2: in them. Long-standing concerns recur. Emotionally important relationships show up repeatedly.
1:27:09
Speaker 2: Memories can be incorporated within days of an event or
1:27:12
Speaker 2: reappear much later. That organisation suggests that the sleeping brain
1:27:17
Speaker 2: is not simply producing arbitrary pictures with no connection to
1:27:21
Speaker 2: the dreamer's history. Spontaneous neural activity and meaningful memory content
1:27:27
Speaker 2: are not mutually exclusive. Internally generated activity may provide part
1:27:32
Speaker 2: of the trigger, while the brain's existing memories, emotions and
1:27:35
Speaker 2: expectations determine what kind of world is constructed around it.
1:27:40
Speaker 2: This is why activation synthesis remains important without needing to
1:27:44
Speaker 2: be treated as the final answer. It helped move dream
1:27:48
Speaker 2: research away from the assumption that every image must contain
1:27:51
Speaker 2: a hidden symbolic message. It placed the physiology of sleep
1:27:55
Speaker 2: at the centre of the explanation, and it offered a
1:27:58
Speaker 2: compelling possibility. Perhaps some dreams feel like strange stories because
1:28:03
Speaker 2: the sleeping brain is constantly trying to make sense of itself.
1:28:07
Speaker 2: Signals appear. Memories join them. Emotion gives them urgency. The
1:28:12
Speaker 2: mind assembles a world around the pieces and before long
1:28:17
Speaker 2: you are standing in a railway station that has somehow
1:28:19
Speaker 2: become a hotel speaking to someone who has not noticed
1:28:22
Speaker 2: that neither of you has any idea how you got there.
1:28:26
Speaker 2: One of the strongest clues about why dreams contain pieces
1:28:29
Speaker 2: of ordinary life comes from something the sleeping brain is
1:28:32
Speaker 2: definitely doing. It is working with memory. Sleep is not
1:28:37
Speaker 2: simply a period in which memory formation pauses until morning.
1:28:41
Speaker 2: Decades of experiments have shown that sleep contributes to several
1:28:45
Speaker 2: forms of learning and memory. Information encountered during the day
1:28:49
Speaker 2: can be strengthened, reorganised and integrated while we sleep, sometimes
1:28:55
Speaker 2: improving what can be remembered or performed later. That established
1:29:00
Speaker 2: finding creates a very tempting possibility. Perhaps dreams are part
1:29:04
Speaker 2: of the process. The important word there is perhaps. There
1:29:09
Speaker 2: is strong evidence that sleep supports memory. There is also
1:29:13
Speaker 2: good evidence that memories enter dreams. What remains much less
1:29:18
Speaker 2: certain is whether the conscious experience of dreaming is itself
1:29:21
Speaker 2: doing the memory work. or whether dreams are something we
1:29:25
Speaker 2: experience while underlying memory processes happen for other reasons. To
1:29:30
Speaker 2: understand the distinction, it helps to begin with memory consolidation.
1:29:35
Speaker 2: A new memory is not simply recorded once and then
1:29:37
Speaker 2: stored permanently in finished form. When something is learned, the
1:29:42
Speaker 2: resulting memory can initially be fragile. Over time, interacting processes
1:29:47
Speaker 2: stabilise it, reorganise it and connect it with information already
1:29:52
Speaker 2: stored in the brain. This collection of processes is known
1:29:56
Speaker 2: as memory consolidation. The hippocampus plays an especially important role
1:30:01
Speaker 2: in many memories for events, places and relationships. During waking experience,
1:30:08
Speaker 2: patterns of activity within hippocampal networks can represent aspects of
1:30:12
Speaker 2: where an animal is, what it is doing and how
1:30:16
Speaker 2: events relate to one another. Remarkably, some of those patterns
1:30:20
Speaker 2: can appear again later. Experiments by neuroscientists including Matthew Wilson
1:30:25
Speaker 2: and Bruce McNaughton helped demonstrate this using recordings from groups
1:30:29
Speaker 2: of neurons in the hippocampus of rats. When the animals
1:30:33
Speaker 2: explored an environment, particular sequences of neurons became active. Later,
1:30:39
Speaker 2: during periods of rest and sleep, related patterns were reactivated.
1:30:44
Speaker 2: The brain appeared, in a sense, to revisit aspects of
1:30:48
Speaker 2: earlier experience. This phenomenon is often called neural replay. Replay
1:30:54
Speaker 2: should not be imagined as a tiny film of the
1:30:57
Speaker 2: day's events being projected somewhere inside the brain. The timing
1:31:02
Speaker 2: can be compressed. Sequences can be reorganised. Some aspects may
1:31:07
Speaker 2: be strengthened while others are not. But the important discovery
1:31:11
Speaker 2: is that information associated with waking experience can become active
1:31:16
Speaker 2: again when the external experience is long over. Much of
1:31:20
Speaker 2: the clearest hippocampal replay associated with memory consolidation occurs during
1:31:26
Speaker 2: non-rapid eye movement sleep, particularly alongside brief events known as
1:31:31
Speaker 2: sharp wave ripples. These coordinated bursts provide opportunities for communication
1:31:37
Speaker 2: between the hippocampus and wider cortical networks. Over repeated periods
1:31:42
Speaker 2: of reactivation, information may become better integrated with more distributed
1:31:47
Speaker 2: stores of knowledge. In broad terms, yesterday's new experience can
1:31:52
Speaker 2: begin becoming part of everything the brain already knows. This
1:31:56
Speaker 2: makes the relationship with dreaming particularly intriguing. Sleep researchers Robert
1:32:01
Speaker 2: Stickgold and Erin Wamsley have examined whether recently learned experiences
1:32:06
Speaker 2: appear within dreams, and whether that incorporation relates to later
1:32:10
Speaker 2: memory performance. In one well-known line of experiments, Participants learned
1:32:16
Speaker 2: to navigate a virtual maze before being allowed to sleep
1:32:19
Speaker 2: or rest. Researchers later asked about the thoughts or dreams
1:32:24
Speaker 2: occurring during that period. Some participants reported experiences connected with
1:32:29
Speaker 2: the maze. These were not necessarily realistic replays. Someone might
1:32:34
Speaker 2: dream about being inside the maze. Another person might report
1:32:38
Speaker 2: something much more loosely connected, such as thinking about music
1:32:42
Speaker 2: associated with the task or imagining an environment that shared
1:32:47
Speaker 2: some of its features. Intriguingly, participants who reported task-related dreams
1:32:53
Speaker 2: sometimes showed greater improvement when navigating the maze later. That sounds,
1:32:59
Speaker 2: at first, like wonderfully neat evidence that dreaming helps memory.
1:33:05
Speaker 2: But the interpretation requires care. The experiment shows an association.
1:33:11
Speaker 2: Dreaming about the task could indicate that the brain was
1:33:14
Speaker 2: strongly reactivating the newly learned material, and that same reactivation
1:33:18
Speaker 2: might improve later performance. The conscious dream may therefore be
1:33:23
Speaker 2: a sign that memory processing is occurring. It does not
1:33:27
Speaker 2: necessarily follow that experiencing the dream is what caused the improvement.
1:33:32
Speaker 2: Imagine seeing steam rising from a kettle. The steam tells
1:33:37
Speaker 2: you that heating is occurring. It does not follow that
1:33:40
Speaker 2: the steam is what heated the water. Dream content may
1:33:44
Speaker 2: sometimes provide a visible or at least reportable trace of
1:33:47
Speaker 2: deeper memory operations without being their essential mechanism. Researchers therefore
1:33:53
Speaker 2: often speak more broadly about memory reactivation during sleep. Recently
1:33:58
Speaker 2: acquired information can be revisited without being reconstructed as an
1:34:02
Speaker 2: exact copy of the original event. And that may help
1:34:06
Speaker 2: explain why dreams are such terrible archivists. A dream may
1:34:10
Speaker 2: contain your colleague's face, your grandmother's house, and an argument
1:34:15
Speaker 2: from yesterday, all occurring on a beach you visited when
1:34:18
Speaker 2: you were twelve. None of those elements needs to be
1:34:22
Speaker 2: invented from nothing. They can be drawn from existing memory.
1:34:26
Speaker 2: But the brain does not seem obliged to preserve the
1:34:29
Speaker 2: original filing system. Memory itself is reconstructive. The nervous system
1:34:36
Speaker 2: stores relationships, features and distributed patterns rather than keeping a
1:34:41
Speaker 2: perfect video recording of every moment. During sleep, fragments associated
1:34:46
Speaker 2: with different experiences may be activated together. The result, when
1:34:51
Speaker 2: it reaches consciousness as a dream, can feel like somebody
1:34:55
Speaker 2: emptied several boxes of memories onto the floor and then
1:34:58
Speaker 2: assembled a new scene from whichever pieces happen to fit.
1:35:02
Speaker 2: There may even be advantages to this looseness. Memory is
1:35:06
Speaker 2: not useful merely because information can be preserved. It is
1:35:10
Speaker 2: useful because information can be organised. Suppose you visit ten
1:35:14
Speaker 2: unfamiliar restaurants. Remembering the precise position of every glass and
1:35:19
Speaker 2: chair is unlikely to matter. Recognising the broader idea of
1:35:24
Speaker 2: how restaurants work is much more useful. The brain benefits
1:35:28
Speaker 2: from extracting patterns. Sleep has been associated not only with
1:35:33
Speaker 2: strengthening particular memories but also with integrating information and under
1:35:37
Speaker 2: some conditions discovering relationships between separate pieces of knowledge. Rather
1:35:43
Speaker 2: than preserving every experience independently, sleeping memory systems may help
1:35:48
Speaker 2: connect new information with old knowledge. This could allow useful
1:35:52
Speaker 2: regularities to become clearer. It might also explain why dream
1:35:56
Speaker 2: imagery occasionally makes remote associations that would be unlikely during
1:36:00
Speaker 2: focused waking thought. Two memories that occurred years apart can
1:36:05
Speaker 2: suddenly occupy the same dream because the sleeping brain is
1:36:09
Speaker 2: not required to respect chronology. Whether that strange conscious combination
1:36:14
Speaker 2: contributes to memory integration or merely accompanies it remains uncertain.
1:36:19
Speaker 2: Forgetting is also part of the story. A brain that
1:36:23
Speaker 2: preserved every detail with equal strength would not necessarily possess
1:36:27
Speaker 2: a better memory. During an ordinary day, enormous quantities of
1:36:32
Speaker 2: information pass through the nervous system. The colour of every
1:36:36
Speaker 2: passing car, the exact position of every object on a
1:36:40
Speaker 2: supermarket shelf, every insignificant background sound, every sentence glimpsed but
1:36:47
Speaker 2: never needed again. Most of it does not deserve permanent storage.
1:36:52
Speaker 2: Useful memory therefore requires selection as well as preservation. Connections
1:36:57
Speaker 2: can be strengthened, reorganised or weakened depending on their significance
1:37:02
Speaker 2: and repeated use. Sleep appears to participate in this broader
1:37:06
Speaker 2: regulation of memory. Although scientists are still investigating precisely how,
1:37:12
Speaker 2: different sleep stages contribute to different forms of remembering and forgetting.
1:37:17
Speaker 2: This is why the phrase sorting memories is useful only
1:37:20
Speaker 2: if it is not taken too literally. There's probably no
1:37:23
Speaker 2: overnight librarian examining each event and placing it into the
1:37:27
Speaker 2: correct mental drawer. The process is distributed across networks of neurons.
1:37:32
Speaker 2: Some patterns are reactivated. Connections between neurons change. Information becomes
1:37:38
Speaker 2: integrated with older knowledge. Certain details become more accessible. Others
1:37:43
Speaker 2: may weaken. And occasionally some of this activity appears to
1:37:47
Speaker 2: enter conscious experience as a dream. That gives memory processing
1:37:52
Speaker 2: an unusually strong place among scientific explanations of dream content.
1:37:57
Speaker 2: It helps explain why recent experiences appear in dreams. It
1:38:01
Speaker 2: helps explain why old memories return. It provides a plausible
1:38:05
Speaker 2: route by which unrelated people and places become combined. And
1:38:09
Speaker 2: it connects dreaming with one of the most firmly established
1:38:12
Speaker 2: functions of sleep itself. But one mystery remains. If all
1:38:17
Speaker 2: of this memory processing can happen through neural reactivation, changing
1:38:21
Speaker 2: synapses and communication between the hippocampus and cortex, why should
1:38:26
Speaker 2: there also be an experience story? Why should reorganizing memories
1:38:30
Speaker 2: feel like being late for a train with someone from
1:38:32
Speaker 2: primary school in a city you visited ten years ago?
1:38:36
Speaker 2: At present, science does not have a definitive answer. Sleep
1:38:40
Speaker 2: unquestionably helps organise memory. Memories unquestionably provide material for dreams.
1:38:48
Speaker 2: Dreaming about newly learned information can sometimes accompany better later performance,
1:38:53
Speaker 2: but none of that yet proves that consciousness must be
1:38:56
Speaker 2: present for the memory benefits to occur. The sleeping brain
1:39:00
Speaker 2: may be sorting parts of yesterday, the dream may be
1:39:03
Speaker 2: involved in that work, or it may be what some
1:39:06
Speaker 2: of that work happens to feel like from the inside.
1:39:09
Speaker 2: For now, those possibilities remain carefully and rather appropriately unsorted.
1:39:15
Speaker 2: Dreams have a peculiar habit of caring about things that
1:39:18
Speaker 2: matter to us. A completely ordinary day may contain thousands
1:39:22
Speaker 2: of small details that never appear again. The exact shape
1:39:25
Speaker 2: of a mug. The number of cars passed on the
1:39:28
Speaker 2: way home. A sentence overheard in a shop. The colour
1:39:32
Speaker 2: of a stranger's coat. Yet a difficult conversation, an approaching deadline,
1:39:38
Speaker 2: an argument with someone close, or the memory of an
1:39:41
Speaker 2: embarrassing mistake can somehow follow us into sleep. not always directly.
1:39:46
Speaker 2: The argument may become a different conflict entirely. The deadline
1:39:50
Speaker 2: may turn into a dream about missing a train. The
1:39:53
Speaker 2: embarrassing mistake may reappear as the much more dramatic experience
1:39:56
Speaker 2: of arriving somewhere important while wearing something completely inappropriate. The
1:40:02
Speaker 2: details change. The emotion often survives. This tendency has encouraged
1:40:06
Speaker 2: a long-standing idea in dream research. Perhaps dreaming is involved
1:40:11
Speaker 2: in processing emotional experience. there is good reason to take
1:40:15
Speaker 2: the possibility seriously. Dream reports frequently contain strong emotion, including fear, anxiety, anger, affection,
1:40:24
Speaker 2: excitement and sadness. Experiences that carry emotional significance during waking
1:40:30
Speaker 2: life also appear disproportionately likely to influence dream content, compared
1:40:35
Speaker 2: with entirely trivial events. The relationship is rarely a perfect replay.
1:40:41
Speaker 2: A stressful meeting does not necessarily return as the same room,
1:40:45
Speaker 2: the same people and the same conversation. Instead, emotional themes
1:40:50
Speaker 2: can be transformed. Concern about failure might become being unprepared
1:40:54
Speaker 2: for an examination. Conflict within a relationship might appear as separation,
1:40:59
Speaker 2: pursuit or being unable to reach somebody. A feeling can
1:41:03
Speaker 2: survive even when the original event has almost completely disappeared.
1:41:07
Speaker 2: Psychologist Rosalind Cartwright spent decades examining relationships between dreaming, mood
1:41:13
Speaker 2: and emotional adaptation. Her research included people experiencing difficult life events,
1:41:19
Speaker 2: including marital separation and depression. Cartwright was interested in whether
1:41:24
Speaker 2: the way emotional material appeared within dreams might relate to
1:41:27
Speaker 2: how successfully people adjusted over time. Some of her work
1:41:31
Speaker 2: suggested that dreaming may help combine difficult emotional experiences with
1:41:35
Speaker 2: older memories and existing knowledge. Rather than simply replaying distress,
1:41:41
Speaker 2: the sleeping mind might gradually place the experience within a
1:41:44
Speaker 2: broader personal context. That general idea fits with something already
1:41:48
Speaker 2: known about sleep. Sleep contributes to emotional regulation. A poor
1:41:54
Speaker 2: night's sleep can make the following day feel more difficult.
1:41:57
Speaker 2: Emotional reactions can become stronger. Irritability can increase. Threatening or
1:42:03
Speaker 2: negative information can become harder to regulate. Over longer periods,
1:42:08
Speaker 2: healthy sleep appears to support the brain systems involved in
1:42:11
Speaker 2: managing emotion. The more difficult question is whether dreaming itself
1:42:16
Speaker 2: performs some of that regulation. One influential attempt to explain
1:42:20
Speaker 2: the connection became known as the Sleep to Remember, Sleep
1:42:23
Speaker 2: to Forget hypothesis. The framework is associated particularly with neuroscientist
1:42:29
Speaker 2: Matthew Walker and Elsvander Helm. The phrase does not mean
1:42:33
Speaker 2: that sleep simply deletes unpleasant memories. quite the opposite. The
1:42:38
Speaker 2: proposal is that sleep, and especially rapid eye movement sleep,
1:42:42
Speaker 2: may help preserve information about an emotional event while gradually
1:42:46
Speaker 2: reducing some of the emotional intensity attached to it. The
1:42:50
Speaker 2: memory remains, the sting may soften. Imagine an unpleasant event
1:42:55
Speaker 2: from years ago. You may still remember what happened perfectly well,
1:42:59
Speaker 2: yet recalling it no longer produces the same physical and
1:43:03
Speaker 2: emotional reaction that it did the following morning. One possibility
1:43:07
Speaker 2: is that repeated processing during sleep contributes to that separation
1:43:11
Speaker 2: between the informational content of a memory and its original
1:43:15
Speaker 2: emotional charge. Rapid eye movement sleep provides an intriguing neurochemical
1:43:20
Speaker 2: environment for such processing. During ordinary wakefulness, the neurotransmitter norepinephrine
1:43:27
Speaker 2: helps regulate arousal, attention and responses to important events. During
1:43:32
Speaker 2: rapid eye movement sleep, activity within the brain's major norepinephrine-producing
1:43:37
Speaker 2: system becomes extraordinarily low. Neurons in the locus coeruleus, a
1:43:42
Speaker 2: small brainstem region that provides norepinephrine to much of the brain,
1:43:46
Speaker 2: become almost silent during this stage. At the same time,
1:43:50
Speaker 2: emotional and memory-related networks can remain highly active. That combination
1:43:56
Speaker 2: attracted considerable scientific interest. Perhaps emotionally important memories can be
1:44:01
Speaker 2: reactivated in a brain that is temporarily operating with very
1:44:04
Speaker 2: little of one of the chemicals strongly associated with alertness
1:44:08
Speaker 2: and stress, in principle, that might allow difficult material to
1:44:12
Speaker 2: be revisited under different physiological conditions. The brain could reactivate
1:44:17
Speaker 2: the memory without reproducing exactly the same neurochemical state that
1:44:21
Speaker 2: accompanied the original waking experience. It is an elegant idea.
1:44:26
Speaker 2: But elegance is not the same as proof. The sleep-to-remember,
1:44:30
Speaker 2: sleep-to-forget framework remains an influential hypothesis rather than a universal
1:44:36
Speaker 2: law explaining every emotional dream. Sleep and emotion interact through
1:44:41
Speaker 2: many systems, and rapid eye-movement sleep is only one part
1:44:45
Speaker 2: of that relationship. Dream content also refuses to behave as
1:44:49
Speaker 2: neatly as a simple therapeutic theory might predict. Consider recurring
1:44:54
Speaker 2: anxiety dreams. During a stressful period, a person may repeatedly
1:44:58
Speaker 2: dream of being late, lost, trapped, unprepared or unable to
1:45:03
Speaker 2: complete something important. These dreams clearly reflect emotional concerns, but
1:45:09
Speaker 2: it does not automatically follow that each repetition is successfully
1:45:12
Speaker 2: resolving them. Sometimes distress appears to persist. Nightmares make that
1:45:18
Speaker 2: difficulty even clearer. A nightmare can wake someone frightened, sweating
1:45:23
Speaker 2: and alert. when nightmares become frequent, they can disrupt sleep itself.
1:45:29
Speaker 2: People may begin to fear going to bed. Poor sleep
1:45:32
Speaker 2: can then worsen daytime emotional regulation, producing a cycle in
1:45:36
Speaker 2: which distress during the day and distress during the night
1:45:39
Speaker 2: reinforce one another. This is particularly important in conditions involving
1:45:44
Speaker 2: recurrent nightmares after traumatic experiences. In such cases, Dreaming does
1:45:50
Speaker 2: not look like a simple process in which difficult emotions
1:45:53
Speaker 2: are steadily weakened night after night. The system can become stuck.
1:45:59
Speaker 2: The dream may repeatedly return to themes of threat without
1:46:03
Speaker 2: producing obvious emotional relief. That complication does not mean emotional
1:46:08
Speaker 2: processing has nothing to do with dreams. It means that
1:46:11
Speaker 2: the relationship is probably more complex than the reassuring idea
1:46:15
Speaker 2: that every bad dream is somehow good for you. An
1:46:18
Speaker 2: unpleasant dream is not automatically therapy. Sometimes it may be
1:46:22
Speaker 2: part of healthy emotional processing. Sometimes it may reflect unresolved stress.
1:46:28
Speaker 2: Sometimes it may simply be what emotional brain activity feels
1:46:32
Speaker 2: like during sleep. This brings back an important distinction. There
1:46:36
Speaker 2: is strong evidence that sleep contributes to emotional regulation. There
1:46:41
Speaker 2: is good evidence that emotional experiences influence dream content. There
1:46:46
Speaker 2: are plausible mechanisms linking rapid eye movement, sleep, memory and
1:46:50
Speaker 2: emotional processing. But those findings do not prove that dream
1:46:54
Speaker 2: narratives evolved specifically to regulate emotion. The useful work may
1:46:59
Speaker 2: be taking place within memory and emotional networks, while the
1:47:02
Speaker 2: dream is a conscious accompaniment. Perhaps the brain is reorganising
1:47:07
Speaker 2: emotional memories, and the dream is what some of the
1:47:10
Speaker 2: activity feels like from the inside. The distinction is subtle
1:47:14
Speaker 2: but important. A person might dream of an argument because
1:47:18
Speaker 2: the sleeping brain is reactivating and integrating emotionally significant material.
1:47:23
Speaker 2: That does not necessarily mean the dream story itself is
1:47:26
Speaker 2: required for the integration to occur. The brain may be
1:47:30
Speaker 2: doing the biological work while consciousness receives a strange reconstructed
1:47:34
Speaker 2: version of it. Still, emotional processing explains several persistent features
1:47:40
Speaker 2: of dreams remarkably well. It helps explain why emotionally important
1:47:45
Speaker 2: people appear so often. It helps explain why anxieties return
1:47:49
Speaker 2: in altered forms. It helps explain why a dream about
1:47:52
Speaker 2: something objectively ridiculous can feel overwhelmingly serious while it is happening.
1:47:59
Speaker 2: Dreams seem unusually sensitive to what matters rather than merely
1:48:03
Speaker 2: to what happened. But emotional processing cannot explain every dream.
1:48:08
Speaker 2: Some are mundane, some are joyful. Some are bizarre without
1:48:12
Speaker 2: any obvious emotional theme. Others seem to contain little more
1:48:16
Speaker 2: than fragments of thought. The sleeping brain is doing many
1:48:19
Speaker 2: things at once, and dreaming may emerge from several of them.
1:48:23
Speaker 2: Emotion is almost certainly part of the story. Whether it
1:48:27
Speaker 2: is the reason the story exists at all remains much
1:48:30
Speaker 2: harder to say. Dreams have a curious fondness for trouble.
1:48:34
Speaker 2: You are being chased, but your legs will not work properly.
1:48:38
Speaker 2: You're trying to escape from a building, but every corridor
1:48:41
Speaker 2: leads somewhere unexpected. You're falling, hiding, arguing, searching for someone,
1:48:48
Speaker 2: losing something important, or attempting to complete a task that
1:48:52
Speaker 2: becomes more complicated every time you get close to finishing it.
1:48:57
Speaker 2: Considering that most people spend a large part of their
1:48:59
Speaker 2: waking lives doing fairly ordinary things, dreams can seem strangely
1:49:04
Speaker 2: determined to introduce difficulties. One explanation is that this may
1:49:09
Speaker 2: be exactly the point. Finnish cognitive neuroscientist Antti Revonsuro proposed
1:49:15
Speaker 2: what became known as the threat simulation theory of dreaming.
1:49:19
Speaker 2: The central idea is that dreams may provide a virtual
1:49:22
Speaker 2: environment in which the brain can repeatedly simulate dangerous or
1:49:26
Speaker 2: challenging situations without exposing the body to the actual danger.
1:49:31
Speaker 2: In other words, the sleeping mind may sometimes function rather
1:49:35
Speaker 2: like a biological training simulator. The evolutionary logic is fairly straightforward.
1:49:41
Speaker 2: For most of human history, survival depended partly on responding
1:49:45
Speaker 2: effectively to threats. Predators were one obvious danger, but they
1:49:50
Speaker 2: were hardly the only one. Conflict with other humans, accidents,
1:49:54
Speaker 2: becoming separated from a group, losing resources … Navigating unfamiliar
1:49:59
Speaker 2: terrain and protecting children could all have serious consequences. An
1:50:04
Speaker 2: individual who recognised danger quickly and responded appropriately might have
1:50:09
Speaker 2: enjoyed a small survival advantage. If the brain could practice
1:50:13
Speaker 2: some of those responses during sleep, then dreaming might provide
1:50:17
Speaker 2: a relatively safe opportunity to rehearse useful patterns. The dreamer
1:50:21
Speaker 2: can run from the predator without actually meeting one. They
1:50:25
Speaker 2: can recognise hostility without entering a real fight. They can
1:50:29
Speaker 2: practise hiding, escaping or searching without the unfortunate inconvenience of
1:50:34
Speaker 2: having to spend every night being genuinely pursued through the forest.
1:50:39
Speaker 2: There is certainly something about ordinary dream content that makes
1:50:42
Speaker 2: the idea attractive. Threatening events are common. Dreamers frequently report
1:50:48
Speaker 2: being chased, attacked or confronted. Others dream about falling, losing
1:50:54
Speaker 2: control of a vehicle, becoming trapped, missing an important deadline,
1:50:58
Speaker 2: being unable to find someone, or discovering that an apparently
1:51:02
Speaker 2: simple situation has gone catastrophically wrong. The threats are not
1:51:07
Speaker 2: always physical. Social danger matters to human beings as well.
1:51:12
Speaker 2: Being humiliated, rejected, criticised or excluded can carry enormous emotional weight,
1:51:18
Speaker 2: and dreams regularly construct situations involving exactly those possibilities. Some
1:51:24
Speaker 2: of these experiences resemble problems humans may have faced for
1:51:28
Speaker 2: thousands of generations. Others have been thoroughly modernised. An ancestral
1:51:33
Speaker 2: human probably did not dream about forgetting the password for
1:51:37
Speaker 2: an important presentation five minutes before a meeting. But the
1:51:42
Speaker 2: underlying feeling of being unprepared in front of other people
1:51:45
Speaker 2: may be considerably older than the laptop. Threat simulation theory
1:51:49
Speaker 2: suggests that what matters is not necessarily the precise surface detail.
1:51:54
Speaker 2: The deeper pattern may involve detecting danger, selecting a response
1:51:58
Speaker 2: and attempting to navigate an uncertain situation. There is evidence
1:52:03
Speaker 2: consistent with parts of this idea. Studies of dream reports
1:52:07
Speaker 2: have found that threats, aggression and unpleasant social interactions appear regularly.
1:52:14
Speaker 2: Researchers also examined populations exposed to unusually threatening waking environments
1:52:19
Speaker 2: and found that waking adversity can influence the frequency and
1:52:23
Speaker 2: character of threatening dream content. That fits naturally with the
1:52:28
Speaker 2: possibility that the sleeping brain is especially likely to simulate
1:52:32
Speaker 2: situations it treats as important. But there is a large
1:52:35
Speaker 2: step between showing that dreams contain threats and demonstrating that
1:52:40
Speaker 2: dreaming evolved as a threat training system. Dreams are extraordinarily varied.
1:52:45
Speaker 2: Many contain no obvious danger at all. People dream about conversations, journeys, friends, food, work,
1:52:54
Speaker 2: Childhood homes, fictional situations and events so mundane that recalling
1:52:59
Speaker 2: them can feel slightly disappointing. Some dreams are pleasant. Some
1:53:04
Speaker 2: are emotionally neutral. Some appear to involve almost no coherent
1:53:08
Speaker 2: problem whatsoever. If threat rehearsal were the principal purpose of dreaming,
1:53:13
Speaker 2: scientists would still need to explain this enormous range. There
1:53:18
Speaker 2: is also the more difficult question of whether simulated threats
1:53:21
Speaker 2: actually improve waking behaviour. A person can spend the night
1:53:26
Speaker 2: running desperately from something and wake without having acquired any
1:53:30
Speaker 2: obvious new skill for escaping predators. Demonstrating that rehearsal genuinely
1:53:36
Speaker 2: produces a useful improvement is much harder than showing that
1:53:40
Speaker 2: the rehearsal seems plausible. This is a common difficulty with
1:53:44
Speaker 2: evolutionary explanations. A theory can tell a very convincing story
1:53:49
Speaker 2: about why a trait might have been useful in ancestral environments.
1:53:53
Speaker 2: but plausibility is not proof that natural selection actually produced
1:53:57
Speaker 2: that trait for that reason. Dreams do not fossilise. We
1:54:02
Speaker 2: cannot collect dream reports from humans living 50,000 years ago
1:54:06
Speaker 2: and compare their survival with that of neighbours who dream differently.
1:54:10
Speaker 2: Researchers therefore have to approach evolutionary claims indirectly, through modern behaviour,
1:54:16
Speaker 2: comparative evidence, neuroscience and carefully constructed predictions. Threat simulation remains
1:54:23
Speaker 2: an intriguing hypothesis, but it should not be mistaken for
1:54:27
Speaker 2: a demonstrated history of why dreaming evolved. A very different
1:54:31
Speaker 2: simulation idea has appeared more recently. Neuroscientist Eric Howell proposed
1:54:37
Speaker 2: what he calls the overfitted brain hypothesis. The inspiration comes
1:54:41
Speaker 2: partly from machine learning. Imagine training a computer system to
1:54:45
Speaker 2: recognise dogs by showing it thousands of examples. If the
1:54:49
Speaker 2: system learns useful general features, It may successfully recognise dogs
1:54:54
Speaker 2: it has never seen before. But there is another possibility.
1:54:58
Speaker 2: It can learn the training examples too precisely. Instead of
1:55:02
Speaker 2: developing a flexible understanding, it becomes specialised for the particular
1:55:06
Speaker 2: images it was shown. When presented with something slightly different,
1:55:11
Speaker 2: performance becomes worse. This problem is called overfitting. A system
1:55:17
Speaker 2: can become excellent at remembering its training material while becoming
1:55:21
Speaker 2: poor at dealing with the wider world. Machine learning researchers
1:55:26
Speaker 2: often try to reduce overfitting by introducing variation. Training data
1:55:31
Speaker 2: can be altered, distorted or made noisier so that the
1:55:36
Speaker 2: system cannot rely too heavily on narrow patterns. It is
1:55:40
Speaker 2: forced to learn broader features that generalise beyond the original examples.
1:55:45
Speaker 2: Hall wondered whether dreaming might accomplish something loosely comparable for
1:55:49
Speaker 2: biological brains. Waking life contains repetition. We travel familiar routes,
1:55:56
Speaker 2: see familiar rooms, perform familiar tasks, interact with the same
1:56:00
Speaker 2: physical laws day after day. The brain is continually learning
1:56:05
Speaker 2: from this structured stream of experience. The overfitted brain hypothesis
1:56:09
Speaker 2: suggests that dreams may introduce deliberately unusual variation into that
1:56:13
Speaker 2: learning process. and dreams are certainly good at unusual variation.
1:56:18
Speaker 2: People change identity. Buildings combine. Distances make little sense. Events
1:56:25
Speaker 2: occur in impossible orders. Physics occasionally appears to have taken
1:56:29
Speaker 2: the night off. From the perspective of ordinary waking accuracy,
1:56:33
Speaker 2: these distortions look like mistakes. From the perspective of a
1:56:37
Speaker 2: system trying not to learn the waking world too rigidly,
1:56:40
Speaker 2: perhaps distortion could sometimes be useful. the dream would act
1:56:44
Speaker 2: a little like corrupted training data. Instead of another perfectly
1:56:50
Speaker 2: ordinary day, the brain receives strange combinations and altered versions
1:56:54
Speaker 2: of familiar patterns. A school becomes a shopping centre. A
1:56:59
Speaker 2: friend appears in a city they have never visited. Gravity
1:57:02
Speaker 2: behaves differently. A routine social situation becomes unpredictable. By disrupting
1:57:08
Speaker 2: ordinary regularities, Dream experience might encourage more flexible representations that
1:57:14
Speaker 2: work across a wider variety of situations. It is a
1:57:18
Speaker 2: clever idea. It is also, at present, speculative. The overfitted
1:57:24
Speaker 2: brain hypothesis is much newer than many major theories of dreaming,
1:57:28
Speaker 2: and there is far less direct evidence supporting it than
1:57:31
Speaker 2: there is for the broader finding that sleep itself contributes
1:57:35
Speaker 2: to learning and memory. The analogy with machine learning is useful.
1:57:40
Speaker 2: But a useful analogy is not automatically a biological mechanism.
1:57:44
Speaker 2: Human brains and artificial neural networks share some broad principles,
1:57:49
Speaker 2: but they are not interchangeable systems. Still, the theory raises
1:57:53
Speaker 2: an interesting possibility about one of the strangest properties of dreams.
1:57:57
Speaker 2: Perhaps their bizarreness is not necessarily a defect. Perhaps being
1:58:01
Speaker 2: unrealistic could sometimes be useful. This makes threat simulation theory
1:58:06
Speaker 2: and the overfitted brain hypothesis similar in one broad respect.
1:58:10
Speaker 2: while remaining fundamentally different ideas. Both treat dreams as simulations,
1:58:16
Speaker 2: but they propose different reasons for the simulation. Threat simulation
1:58:20
Speaker 2: theory emphasises rehearsal. The dream produces situations involving danger or challenge.
1:58:26
Speaker 2: so that systems for perception and action can repeatedly engage
1:58:30
Speaker 2: with biologically important problems. The overfitted brain hypothesis emphasises variation.
1:58:37
Speaker 2: The dream distorts ordinary experience so that learning systems do
1:58:41
Speaker 2: not become excessively specialised to the repetitive patterns of waking life.
1:58:46
Speaker 2: One says that dreams may help us practise important situations.
1:58:51
Speaker 2: The other says that dreams may help prevent our models
1:58:53
Speaker 2: of the world becoming too narrow, Both could conceivably capture
1:58:58
Speaker 2: part of what is happening. Neither has been established as
1:59:01
Speaker 2: the single function of dreams, and this reveals a problem
1:59:05
Speaker 2: that appears repeatedly in dream science. Almost every striking feature
1:59:09
Speaker 2: of dreaming can support more than one explanation. Threatening dreams
1:59:14
Speaker 2: might be rehearsal, or they might simply reflect emotionally important memories.
1:59:19
Speaker 2: Bizarre dreams might encourage flexible learning, or they might emerge
1:59:24
Speaker 2: because normal sensory constraints and executive monitoring are reduced. Simulated
1:59:30
Speaker 2: worlds might serve a function, or they might be what
1:59:33
Speaker 2: consciousness looks like when memory, emotion and perception operate under
1:59:38
Speaker 2: unusual sleeping conditions. The dream itself cannot tell us which
1:59:42
Speaker 2: explanation is correct. It merely provides the phenomenon that needs explaining.
1:59:48
Speaker 2: Perhaps some nights the brain rehearses danger. Perhaps some dreams
1:59:52
Speaker 2: introduce useful variations. Perhaps both happen occasionally, without either being
1:59:57
Speaker 2: the universal reason dreaming exists. Whatever the answer, the sleeping
2:00:02
Speaker 2: brain certainly seems capable of creating one of the most
2:00:05
Speaker 2: peculiar training environments imaginable. It removes the real world, rearranges
2:00:11
Speaker 2: the rules, adds a problem, occasionally removes the flaw, and
2:00:15
Speaker 2: then leaves you to see what you do. Some dreams
2:00:18
Speaker 2: are so common that people who have never met can
2:00:21
Speaker 2: describe remarkably similar experiences, falling, being chased, running late for
2:00:27
Speaker 2: something important, arriving at an examination without having revised, trying
2:00:32
Speaker 2: to move and discovering that the legs will not cooperate,
2:00:36
Speaker 2: realising that something essential has been forgotten, or the particularly
2:00:41
Speaker 2: unpleasant experience of feeling that teeth are loose, crumbling, breaking
2:00:45
Speaker 2: or disappearing from the mouth. These themes appear often enough
2:00:49
Speaker 2: that it is tempting to assume they must contain universal meanings.
2:00:54
Speaker 2: Dream researchers have spent decades examining whether that is actually true.
2:00:59
Speaker 2: Michael Schriedel has studied large collections of dream reports and
2:01:02
Speaker 2: recurring themes, while Antonio Zedra has carried out extensive research
2:01:07
Speaker 2: into nightmares, recurrent dreams, and the emotional structure of dreaming.
2:01:13
Speaker 2: Their work, along with that of many other sleep researchers,
2:01:17
Speaker 2: shows that dream content is not completely random. Certain themes
2:01:21
Speaker 2: do appear again and again. but repetition does not automatically
2:01:26
Speaker 2: mean symbolism. Humans share many of the same concerns. We
2:01:30
Speaker 2: all experience uncertainty. We all know what it is like
2:01:34
Speaker 2: to be evaluated, embarrassed, threatened, delayed, physically uncomfortable or worried
2:01:40
Speaker 2: that something important has been forgotten. We also share broadly
2:01:44
Speaker 2: similar bodies. That combination alone can produce recurring dream situations
2:01:49
Speaker 2: without requiring a hidden dictionary. in which every object stands
2:01:53
Speaker 2: for one fixed meaning. Consider dreams about being late. A
2:01:59
Speaker 2: person may be trying desperately to reach an airport, a meeting,
2:02:02
Speaker 2: a wedding or an examination. Something keeps going wrong. The
2:02:07
Speaker 2: train does not arrive. The road becomes impossible to navigate.
2:02:11
Speaker 2: The shoes disappear. The building seems to move further away
2:02:15
Speaker 2: every time the dreamer gets closer. It is easy to
2:02:18
Speaker 2: see why these dreams might overlap with waking concerns about responsibility,
2:02:23
Speaker 2: evaluation and loss of control. Being late in ordinary life
2:02:28
Speaker 2: can have consequences. Missing an examination matters. Missing a flight matters.
2:02:35
Speaker 2: Failing to arrive when other people expect you matters. So
2:02:38
Speaker 2: the emotional structure of the dream is familiar even when
2:02:41
Speaker 2: the details are absurd. But the same dream does not
2:02:45
Speaker 2: have to mean the same thing for everyone. For one person,
2:02:49
Speaker 2: being late might reflect current work pressure. For another, it
2:02:54
Speaker 2: may relate to a fear of disappointing someone. For someone else,
2:02:58
Speaker 2: it may simply be the sleeping brain borrowing a familiar
2:03:01
Speaker 2: kind of stressful situation. There is no scientifically established rule
2:03:06
Speaker 2: stating that dreams of lateness always reveal one particular psychological problem.
2:03:12
Speaker 2: Dreams about examinations are similar. People can continue having them
2:03:16
Speaker 2: years or even decades after leaving school. In the dream
2:03:20
Speaker 2: there is often an unpleasant discovery. There is an examination today.
2:03:25
Speaker 2: You have forgotten to revise. Perhaps you have not attended
2:03:28
Speaker 2: the class all year. You do not know where the
2:03:31
Speaker 2: room is. And for reasons never adequately explained by the dream,
2:03:35
Speaker 2: this examination remains extremely important despite the fact that waking
2:03:39
Speaker 2: life has moved on. The emotional ingredients are obvious. evaluation, unpreparedness, consequences,
2:03:49
Speaker 2: loss of control. Those themes remain relevant long after school ends,
2:03:54
Speaker 2: which may help explain why the dream itself can survive.
2:03:58
Speaker 2: Another extremely common theme is falling. Falling dreams can occur
2:04:02
Speaker 2: during established sleep, but they are also often confused with
2:04:06
Speaker 2: something slightly different that happens during the transition into sleep.
2:04:10
Speaker 2: A hypnic jerk is a sudden involuntary muscle contraction, that
2:04:14
Speaker 2: can occur as a person is drifting from wakefulness into sleep.
2:04:19
Speaker 2: Sometimes it is accompanied by the sensation of stumbling or falling.
2:04:23
Speaker 2: The body suddenly twitches and the person wakes with the
2:04:27
Speaker 2: feeling that they have stepped off a ledge that was
2:04:29
Speaker 2: never there. Hypnic jerks are common and generally harmless. They
2:04:34
Speaker 2: are not the same thing as every dream involving falling.
2:04:37
Speaker 2: A person can have a fully developed dream of falling
2:04:40
Speaker 2: from a building, slipping from a cliff or dropping through
2:04:44
Speaker 2: the sky without experiencing a hypnic jerk at all. The
2:04:48
Speaker 2: theme may emerge from the brain system for movement, balance
2:04:52
Speaker 2: and bodily sensation, from emotional concerns, or from several influences
2:04:57
Speaker 2: at once. Again, there is no need to assume that
2:05:00
Speaker 2: falling always means one specific thing. Then there are teeth dreams.
2:05:06
Speaker 2: Few ordinary dream themes have attracted more confident explanations. A
2:05:10
Speaker 2: quick search of popular dream interpretation can produce claims involving confidence, ageing, money, grief, embarrassment, death, communication, attractiveness,
2:05:22
Speaker 2: or major life change. The problem is that there is
2:05:25
Speaker 2: no scientifically established universal meaning. Teeth dreams are genuinely common.
2:05:31
Speaker 2: Researchers have documented them repeatedly, but showing that many people
2:05:36
Speaker 2: dream about damaged or missing teeth does not tell us why.
2:05:40
Speaker 2: One possibility is that bodily sensations contribute. Clenching the jaw,
2:05:45
Speaker 2: grinding the teeth or experiencing discomfort during sleep could sometimes
2:05:49
Speaker 2: influence dream imagery. Another possibility is that teeth carry obvious
2:05:55
Speaker 2: emotional associations involving appearance, vulnerability and physical integrity. It may
2:06:01
Speaker 2: also be that dreams about teeth are memorable precisely because
2:06:05
Speaker 2: they are disturbing. What science cannot currently justify, is a
2:06:11
Speaker 2: claim that every person dreaming of a loose tooth is
2:06:14
Speaker 2: receiving the same psychological message. The broader explanation offered by
2:06:20
Speaker 2: the continuity hypothesis is much less dramatic. Waking life tends
2:06:25
Speaker 2: to continue into dreams, not as a perfect recording, but
2:06:29
Speaker 2: through recurring concerns, memories, relationships and emotional themes. Something that
2:06:36
Speaker 2: matters during the day is more likely to influence dreams
2:06:38
Speaker 2: than something entirely insignificant. Recent experiences often appear particularly strongly.
2:06:46
Speaker 2: Researchers sometimes use the term day residue for elements of
2:06:49
Speaker 2: waking life that enter dreams shortly after the original event.
2:06:53
Speaker 2: A conversation from yesterday may reappear. A journey may influence
2:06:58
Speaker 2: the setting. Someone recently encountered may suddenly become a dream character.
2:07:03
Speaker 2: There is also evidence for what has been called the
2:07:05
Speaker 2: dream lag effect. Some studies have found that experiences may
2:07:09
Speaker 2: become more likely to appear in dreams several days after
2:07:13
Speaker 2: they occurred, rather than only on the immediately following night.
2:07:18
Speaker 2: The exact timing is not perfectly reliable, and the effect
2:07:21
Speaker 2: has not appeared equally strongly in every study. So it
2:07:25
Speaker 2: should not be treated as though the sleeping brain follows
2:07:28
Speaker 2: a neat calendar. But the broader point remains useful. Dream
2:07:33
Speaker 2: content can draw from several layers of memory. Something from
2:07:37
Speaker 2: yesterday can mix with something from last week and something
2:07:40
Speaker 2: from childhood. That combination helps explain why dream scenes can
2:07:45
Speaker 2: feel familiar without corresponding to anything that actually happened. The
2:07:50
Speaker 2: same principle applies to being chased. Humans understand pursuit instinctively.
2:07:55
Speaker 2: It contains danger, urgency and uncertainty. A dream does not
2:08:01
Speaker 2: need to invent a complicated explanation for why running matters.
2:08:05
Speaker 2: The emotional logic arrives immediately. The same is true of
2:08:09
Speaker 2: being trapped, lost or unable to move. These are situations
2:08:14
Speaker 2: that naturally produce strong emotional responses. which may make them
2:08:18
Speaker 2: especially easy for the dreaming brain to construct, and especially
2:08:22
Speaker 2: likely for the waking mind to remember. At the more
2:08:26
Speaker 2: distressing end of this spectrum are nightmares. An occasional nightmare
2:08:30
Speaker 2: is extremely common. A frightening dream may involve pursuit, injury, threat, helplessness,
2:08:37
Speaker 2: or the loss of somebody important. Usually the person wakes, recovers,
2:08:42
Speaker 2: and life continues. Nightmare disorder is different. Here, distressing dreams
2:08:48
Speaker 2: recur often enough to cause significant problems. They may repeatedly
2:08:52
Speaker 2: interrupt sleep, produce anxiety about going to bed, or impair
2:08:56
Speaker 2: daytime well-being. This distinction matters because a frightening dream is
2:09:00
Speaker 2: not automatically evidence of a sleep disorder. Frequency, intensity and
2:09:06
Speaker 2: disruption are what make the difference clinically. Recurring themes therefore
2:09:11
Speaker 2: reveal something important about dreaming. Dreams are not completely arbitrary.
2:09:15
Speaker 2: They repeatedly return to certain kinds of human problems. Threat, evaluation, embarrassment,
2:09:22
Speaker 2: loss of control, physical vulnerability, forgetting, being unable to reach
2:09:27
Speaker 2: something that matters. These themes make sense in creatures whose
2:09:31
Speaker 2: waking lives are filled with goals, relationships, memories and bodies
2:09:35
Speaker 2: that occasionally behave inconveniently. But regularity does not tell us
2:09:40
Speaker 2: why the dreams exist. A chase dream could be a
2:09:43
Speaker 2: simulation of danger. It could reflect emotional processing. It could
2:09:47
Speaker 2: emerge from memory fragments interacting with fear systems. Or it
2:09:52
Speaker 2: could simply be an especially natural story for a sleeping
2:09:55
Speaker 2: brain to construct once the feeling of threat has appeared.
2:09:59
Speaker 2: The same ambiguity applies to teeth, falling, examinations and lateness.
2:10:04
Speaker 2: The themes are real. The universal dictionary is not. And
2:10:08
Speaker 2: perhaps that is why dreams remain so tempting to interpret.
2:10:12
Speaker 2: They feel personal enough to matter. familiar enough to recognise,
2:10:16
Speaker 2: and strange enough to make us wonder whether something deeper
2:10:19
Speaker 2: must be hiding underneath. Sometimes there may be. Sometimes the
2:10:23
Speaker 2: brain may simply have noticed that being late for an
2:10:26
Speaker 2: examination with no teeth while falling down a staircase is
2:10:29
Speaker 2: a remarkably efficient way to get your attention. Most dreams
2:10:34
Speaker 2: contain a rather convincing illusion. Whatever is happening seems to
2:10:38
Speaker 2: be real. You may be standing somewhere impossible, talking to
2:10:41
Speaker 2: somebody who should not be there, or attempting to solve
2:10:44
Speaker 2: a problem that makes very little sense. Yet the thought
2:10:48
Speaker 2: that would instantly explain everything rarely appears. I am dreaming. Sometimes, however,
2:10:54
Speaker 2: it does. The dream continues. The sleeper remains asleep. The
2:10:59
Speaker 2: strange landscape does not necessarily disappear. But suddenly, the person
2:11:04
Speaker 2: inside it knows what is happening. This is lucid dreaming.
2:11:08
Speaker 2: A lucid dream is a dream in which the dreamer
2:11:11
Speaker 2: becomes aware. while the dream is still occurring, that the
2:11:14
Speaker 2: experience is a dream. That definition is important because lucidity
2:11:19
Speaker 2: is not the same thing as vividness. A dream can
2:11:22
Speaker 2: be extraordinarily vivid without being lucid. The colours may seem bright,
2:11:27
Speaker 2: the emotions intense and the environment completely convincing, while the
2:11:32
Speaker 2: dreamer still believes every event is actually happening. Lucidity specifically
2:11:37
Speaker 2: involves recognition. Some part of the mind realises that the
2:11:41
Speaker 2: world being experienced is being generated during sleep. That recognition
2:11:46
Speaker 2: can be very brief. A dreamer may notice something impossible,
2:11:51
Speaker 2: understand for a few seconds that they must be dreaming,
2:11:54
Speaker 2: and then lose the insight almost immediately. At other times,
2:11:58
Speaker 2: lucidity can remain stable for longer. The dreamer may deliberately
2:12:03
Speaker 2: decide where to go, what to look at or how
2:12:06
Speaker 2: to respond to a situation. Some people report being able
2:12:09
Speaker 2: to influence aspects of the dream environment as well, but
2:12:12
Speaker 2: control is not required. You can know that you are
2:12:15
Speaker 2: dreaming while discovering that the dream itself has apparently declined
2:12:19
Speaker 2: your request for management access. Lucidity therefore exists on something
2:12:24
Speaker 2: of a spectrum. At one end is a fleeting realisation.
2:12:28
Speaker 2: At the other is sustained awareness accompanied by deliberate choices
2:12:32
Speaker 2: and varying degrees of influence over the experience. For dream researchers,
2:12:37
Speaker 2: This unusual state created an extraordinary opportunity. If a person
2:12:42
Speaker 2: inside a dream knew they were dreaming, perhaps they could
2:12:45
Speaker 2: deliberately send a signal to researchers outside it. Psychophysiologist Stephen
2:12:50
Speaker 2: LaBerge helped turn that idea into an experimental method during
2:12:54
Speaker 2: his work at Stanford University. The problem was obvious. During
2:12:59
Speaker 2: rapid eye movement sleep, most large skeletal muscles are strongly inhibited,
2:13:04
Speaker 2: A sleeping participant cannot simply sit up halfway through a
2:13:08
Speaker 2: dream and announce that the experiment is going well without
2:13:12
Speaker 2: also ending the experiment rather dramatically. The eyes, however, provide
2:13:17
Speaker 2: a useful exception. They remain capable of making large, deliberate
2:13:21
Speaker 2: movements during rapid eye movement sleep. LaBerge and other researchers
2:13:26
Speaker 2: trained lucid dreamers to perform predetermined patterns of eye movements
2:13:30
Speaker 2: after recognising that they had become lucid. For example, a
2:13:34
Speaker 2: dreamer might deliberately look left, then right, then left and
2:13:37
Speaker 2: right again. Those movements could be detected by electrodes positioned
2:13:42
Speaker 2: near the eyes. Before sleeping, the participants and researchers agreed
2:13:47
Speaker 2: on the signal. Later, the sleeper entered rapid eye movement sleep.
2:13:52
Speaker 2: If lucidity occurred, the dreamer performed the agreed eye movement
2:13:56
Speaker 2: pattern from inside the dream. The recording equipment outside detected it.
2:14:02
Speaker 2: This was remarkable because it gave researchers a time marker
2:14:05
Speaker 2: produced intentionally by somebody who was asleep. The participant did
2:14:09
Speaker 2: not have to wake and say, several minutes later, that
2:14:13
Speaker 2: they thought lucidity had begun somewhere around a particular point.
2:14:17
Speaker 2: They could signal it as it happened. Dream research had
2:14:21
Speaker 2: gained something approaching communication across the boundary between waking and dreaming.
2:14:25
Speaker 2: Researchers could then ask lucid dreamers to perform particular actions.
2:14:30
Speaker 2: A participant might signal the beginning of lucidity, deliberately count
2:14:34
Speaker 2: for a period within the dream, perform a movement, or
2:14:37
Speaker 2: carry out another agreed task before signalling again. Scientists could
2:14:42
Speaker 2: compare what the dreamer reported doing with changes measured in breathing,
2:14:46
Speaker 2: eye movements, brain activity or muscle signals. These experiments helped
2:14:51
Speaker 2: demonstrate that dream events could sometimes be linked with physiology
2:14:55
Speaker 2: at identifiable moments rather than reconstructed entirely from memory after awakening.
2:15:01
Speaker 2: Lucid dreaming also offered clues about what changes when a
2:15:05
Speaker 2: person suddenly questions the dream. Ordinary dreaming often contains reduced metacognition.
2:15:11
Speaker 2: The dreamer experiences events but does not examine the experience
2:15:14
Speaker 2: very critically. An impossible building is accepted. A dead relative
2:15:19
Speaker 2: appears and receives no serious investigation. Gravity changes its mind.
2:15:24
Speaker 2: Everyone carries on. During lucidity, some reflective awareness returns. The
2:15:30
Speaker 2: dreamer can inspect the experience and reach a conclusion about
2:15:33
Speaker 2: their own mental state. This is a form of metacognition.
2:15:37
Speaker 2: The person is not merely seeing the dream. They know
2:15:40
Speaker 2: something about the fact that they are seeing it. That
2:15:43
Speaker 2: does not mean every aspect of waking reasoning has returned.
2:15:48
Speaker 2: A lucid dream remains a dream. Thinking may still be unusual.
2:15:53
Speaker 2: Memory for waking intentions can be incomplete. Control may fluctuate.
2:15:58
Speaker 2: The insight can disappear. But one particularly important piece of
2:16:03
Speaker 2: self-knowledge has become available. This world is not the waking world.
2:16:08
Speaker 2: Experiments have since taken the idea of communication even further.
2:16:12
Speaker 2: In a research published in 2021, Teams working across several
2:16:17
Speaker 2: laboratories demonstrated limited two-way communication with people during verified rapid
2:16:22
Speaker 2: eye movement sleep. Researchers including Karen Conkely and Ken Paller
2:16:27
Speaker 2: at Northwestern University collaborated with teams in France, Germany and
2:16:32
Speaker 2: the Netherlands. Participants were sometimes able to receive simple questions
2:16:37
Speaker 2: while asleep and respond without fully waking. Some heard spoken questions.
2:16:43
Speaker 2: Others received signals through different sensory routes. The tasks were
2:16:47
Speaker 2: deliberately simple. A dreamer might be given a basic arithmetic
2:16:51
Speaker 2: problem or a yes or no question. The answer could
2:16:54
Speaker 2: then be communicated through predetermined eye movements or small facial
2:16:57
Speaker 2: muscle contractions. Not every attempt worked. Far from it. Successful
2:17:04
Speaker 2: communication occurred only in a portion of trials, and lucid
2:17:08
Speaker 2: dreaming itself can be difficult to produce reliably in a laboratory.
2:17:12
Speaker 2: But some sleeping participants correctly understood new information presented from
2:17:16
Speaker 2: outside the dream and sent appropriate answers back. That result
2:17:21
Speaker 2: challenged the intuitive picture of dreaming as a completely sealed state.
2:17:26
Speaker 2: The sleeping brain is certainly less responsive to the outside
2:17:29
Speaker 2: world than an awake brain. Yet sensory information is not
2:17:34
Speaker 2: always entirely excluded. Under particular conditions, a question from the
2:17:38
Speaker 2: laboratory can apparently enter an ongoing dream. be processed by
2:17:42
Speaker 2: the sleeper and receive a deliberate response. Some participants later
2:17:47
Speaker 2: described the incoming questions as becoming incorporated into the dream itself.
2:17:52
Speaker 2: A voice from the laboratory might be experienced as a
2:17:55
Speaker 2: voice coming from within the dream environment. The boundary between
2:17:59
Speaker 2: internal and external information was therefore not always obvious from
2:18:03
Speaker 2: the dreamer's perspective. This makes lucid dreaming scientifically valuable for
2:18:08
Speaker 2: a very simple reason. Dreams are private. Normally, researchers have
2:18:13
Speaker 2: to wait until the person wakes and describes what happened.
2:18:17
Speaker 2: Memory can fade. Timing becomes uncertain. Details can be reorganised.
2:18:23
Speaker 2: Lucid dreamers offer a rare opportunity to obtain information while
2:18:27
Speaker 2: the experience is still occurring. The bridge remains narrow. Communication
2:18:32
Speaker 2: is limited. The state can be unstable. But even a
2:18:36
Speaker 2: narrow bridge between a private dream and an external laboratory
2:18:39
Speaker 2: is something dream researchers once did not have. Lucid dreaming
2:18:45
Speaker 2: has also attracted claims that extend far beyond the evidence.
2:18:49
Speaker 2: It is sometimes presented as a way to control every
2:18:52
Speaker 2: detail of a private universe, master complex skills overnight, solve
2:18:56
Speaker 2: any psychological problem or reliably obtain dramatic personal benefits. Scientific
2:19:02
Speaker 2: results are considerably more modest. Some people appear naturally prone
2:19:07
Speaker 2: to lucid dreams, others rarely experience them. Dream control varies enormously.
2:19:14
Speaker 2: Knowing that one is dreaming does not guarantee the ability
2:19:17
Speaker 2: to produce any desired event. Practising a movement inside a
2:19:22
Speaker 2: lucid dream may engage some of the same brain systems
2:19:26
Speaker 2: involved in imagining or performing actions, but that does not
2:19:30
Speaker 2: mean sleeping practice can simply replace waking training. Likewise, there
2:19:35
Speaker 2: is active research into possible uses for nightmares and other
2:19:38
Speaker 2: psychological applications, but there is no reason to treat lucidity
2:19:43
Speaker 2: as a guaranteed therapy. Its most extraordinary feature requires no exaggeration.
2:19:49
Speaker 2: During an ordinary dream, the brain creates a convincing world
2:19:53
Speaker 2: and temporarily mistakes it for reality. During a lucid dream,
2:19:57
Speaker 2: something even stranger happens. The brain creates the world, The
2:20:02
Speaker 2: person inside that world recognises that it has been created.
2:20:08
Speaker 2: And the world does not necessarily vanish. You can look
2:20:11
Speaker 2: around at a street that is not there, speak to
2:20:14
Speaker 2: people generated from memory, feel the ground beneath feet that
2:20:18
Speaker 2: are actually motionless in bed, and understand that the entire
2:20:22
Speaker 2: environment exists only as an ongoing experience within a sleeping brain.
2:20:27
Speaker 2: You have not quite woken up. you have simply become
2:20:31
Speaker 2: awake to the fact that you are dreaming. Watch a
2:20:34
Speaker 2: sleeping dog for long enough, and sooner or later it
2:20:38
Speaker 2: may appear to be doing something rather interesting. The paws twitch,
2:20:43
Speaker 2: the whiskers move. Perhaps there is a faint sound from
2:20:47
Speaker 2: the throat, followed by several small movements of the legs
2:20:51
Speaker 2: that look suspiciously like running. It is almost impossible not
2:20:55
Speaker 2: to imagine the obvious explanations. The dog is dreaming about
2:20:58
Speaker 2: chasing something. Perhaps another dog. Perhaps a rabbit. Perhaps the
2:21:03
Speaker 2: person responsible for opening the refrigerator. The difficulty is that
2:21:08
Speaker 2: the dog cannot wake up and tell us. That creates
2:21:11
Speaker 2: one of the most important problems in studying dreams outside
2:21:14
Speaker 2: adult humans. A person can be awakened in a sleep
2:21:18
Speaker 2: laboratory and asked what they were experiencing. An animal cannot
2:21:24
Speaker 2: provide a verbal dream report. Researchers can record its brain activity,
2:21:29
Speaker 2: observe its movements and identify different stages of sleep. They
2:21:34
Speaker 2: can find remarkably suggestive similarities with sleeping humans, but the
2:21:39
Speaker 2: subjective experience remains inaccessible. Many mammals show recognisable forms of
2:21:45
Speaker 2: rapid eye movement and non-rapid eye movement sleep. Dogs, cats,
2:21:50
Speaker 2: rats and many other mammals pass through changing sleep states
2:21:55
Speaker 2: accompanied by differences in brain activity, eye movements and muscle tone.
2:22:00
Speaker 2: Sleep states resembling rapid eye movement sleep have also been
2:22:04
Speaker 2: identified in birds, although sleep architecture differs between species. This
2:22:10
Speaker 2: shared biology makes it quite plausible that humans are not
2:22:14
Speaker 2: the only animals capable of internally generated experiences during sleep. Plausible, however,
2:22:20
Speaker 2: is not the same as directly demonstrated. Some of the
2:22:23
Speaker 2: most fascinating evidence comes from rats. Neuroscientists Matthew Wilson and
2:22:28
Speaker 2: Bruce McNaughton performed influential experiments examining activity in the hippocampus,
2:22:35
Speaker 2: a brain structure deeply involved in spatial memory. Within the
2:22:39
Speaker 2: hippocampus are neurons often called place cells. These cells become
2:22:43
Speaker 2: active in relation to particular locations within an environment. As
2:22:48
Speaker 2: a rat moves through a space, different patterns of place
2:22:51
Speaker 2: cell activity correspond to different parts of its route. This
2:22:55
Speaker 2: gives researchers a measurable neural representation associated with where the
2:23:00
Speaker 2: animal has been. Wilson and McNaughton found something remarkable when
2:23:05
Speaker 2: rats later rested and slept. Patterns of hippocampal activity associated
2:23:10
Speaker 2: with the animal's earlier waking experiences appeared again. Neural sequences
2:23:15
Speaker 2: linked with exploring an environment were reactivated after the exploration
2:23:20
Speaker 2: had ended. This became famous in simplified descriptions as rats
2:23:25
Speaker 2: replaying mazes while they sleep. And in one sense, that
2:23:29
Speaker 2: is a useful description. The sleeping rat's hippocampus can indeed
2:23:34
Speaker 2: reactivate patterns associated with locations and routes encountered while awake.
2:23:39
Speaker 2: Some later experiments have shown replay occurring in compressed sequences,
2:23:44
Speaker 2: with patterns that unfolded over seconds during waking behaviour, recurring
2:23:48
Speaker 2: much more rapidly during sleep. But there is an important
2:23:52
Speaker 2: line that science cannot currently cross. Neural replay is not
2:23:57
Speaker 2: the same thing as proving that the rat consciously dreams
2:24:00
Speaker 2: of running through the maze. The neurons can tell us
2:24:03
Speaker 2: that spatial information is being reactivated. They cannot tell us
2:24:08
Speaker 2: what that reactivation feels like, or whether it feels like
2:24:12
Speaker 2: anything at all. Perhaps there is a vivid rat experience
2:24:16
Speaker 2: of moving through a familiar environment. Perhaps the reactivation contributes
2:24:21
Speaker 2: to memory processing, without producing anything resembling the conscious dreams
2:24:26
Speaker 2: humans describe. At present, researchers cannot simply ask the rat afterwards.
2:24:32
Speaker 2: This distinction between brain activity and subjective experience matters enormously.
2:24:38
Speaker 2: It also applies to the sleeping dog. During rapid eye
2:24:42
Speaker 2: movement sleep, dogs can show twitches of the paws, face
2:24:46
Speaker 2: and other muscles. These movements occur against the background of
2:24:50
Speaker 2: the reduced skeletal muscle tone typical of rapid eye movement sleep.
2:24:54
Speaker 2: They certainly look like fragments of behaviour, but a twitch
2:24:58
Speaker 2: cannot tell us what is happening inside the animal's experience.
2:25:02
Speaker 2: A paw movement could accompany a dream of running. It
2:25:06
Speaker 2: could accompany some entirely different internal experience. Or it could
2:25:10
Speaker 2: reflect activity within motor circuits without requiring a rich conscious
2:25:14
Speaker 2: scene at all? Watching the movement and inventing the story
2:25:19
Speaker 2: ourselves is very easy. Demonstrating the story scientifically is much harder.
2:25:25
Speaker 2: Birds add another intriguing piece of evidence. Some species show
2:25:29
Speaker 2: sleep-related reactivation of neural patterns associated with behaviour learned while awake.
2:25:36
Speaker 2: Songbirds provide a particularly striking example. Research on birds such
2:25:41
Speaker 2: as zebra finches has found that neural activity related to
2:25:44
Speaker 2: learned song can reappear during sleep. The sleeping bird's brain
2:25:49
Speaker 2: seems to revisit patterns involved in producing vocal sequences it
2:25:53
Speaker 2: practised while awake. Again, this has obvious parallels with memory
2:25:58
Speaker 2: reactivation in mammals, but it leaves the same unanswered question.
2:26:03
Speaker 2: Is the bird experiencing its song? Is there anything resembling
2:26:07
Speaker 2: an auditory dream? Or is the nervous system simply carrying
2:26:11
Speaker 2: out offline processing without a conscious experience attached to it?
2:26:16
Speaker 2: The measurements alone cannot decide. Human babies create an even
2:26:20
Speaker 2: stranger version of the problem. Newborn infants spend a very
2:26:24
Speaker 2: large proportion of their sleep in what is commonly called
2:26:27
Speaker 2: active sleep, a state with several similarities to rapid eye
2:26:31
Speaker 2: movement sleep in adults. The exact organisation changes rapidly during development.
2:26:37
Speaker 2: but active sleep occupies far more of a newborn's sleeping
2:26:41
Speaker 2: time than rapid eye movement sleep does in a typical adult.
2:26:45
Speaker 2: That observation naturally produces a charming question. What could a
2:26:50
Speaker 2: newborn possibly be dreaming about? Unfortunately, it is almost perfectly
2:26:55
Speaker 2: designed to resist an answer. A newborn cannot provide a report,
2:27:00
Speaker 2: and we should not assume that adult style, rapid eye
2:27:04
Speaker 2: movement physiology, automatically produces adult-style dream experience. The mental world
2:27:10
Speaker 2: of a newborn differs enormously from that of an adult.
2:27:14
Speaker 2: A rich adult dream can involve spoken conversations, knowledge of
2:27:19
Speaker 2: social relationships, memories extending back decades, complicated narratives and a
2:27:25
Speaker 2: reasonably stable sense of oneself as a person moving through time.
2:27:29
Speaker 2: A newborn has not yet developed most of those abilities.
2:27:34
Speaker 2: Language has barely begun its long process of development. Autobiographical
2:27:39
Speaker 2: memory is immature. Knowledge of other people, objects, space and
2:27:44
Speaker 2: cause and effect is still being constructed. Even the sense
2:27:48
Speaker 2: of a stable self develops gradually. If infants do experience
2:27:53
Speaker 2: something during active sleep, there is no reason to assume
2:27:57
Speaker 2: that it resembles an adult dream in which somebody misses
2:28:00
Speaker 2: a flight. argues with a colleague and then somehow discovers
2:28:03
Speaker 2: that their childhood home is floating in the Atlantic. The experience,
2:28:08
Speaker 2: if present, could be much simpler. Perhaps sensations, fragments of imagery, movement, sound, emotion.
2:28:17
Speaker 2: But even those possibilities are inferences. We cannot inspect the
2:28:21
Speaker 2: experience itself. Research on older children provides some clues about
2:28:26
Speaker 2: how dreaming develops. Psychologist David Fulkes spent many years studying
2:28:31
Speaker 2: children's dream reports, including carefully controlled awakenings during sleep. His
2:28:36
Speaker 2: work suggested that the complexity of reported dreams changes substantially
2:28:41
Speaker 2: as children develop. Younger children's reports tend, on average, to
2:28:45
Speaker 2: be shorter and simpler than those of older children and adults.
2:28:49
Speaker 2: Rich narratives involving an active dream self, complicated social interaction
2:28:55
Speaker 2: and elaborate sequences become more common as cognitive abilities develop.
2:29:01
Speaker 2: Falks connected these changes with developments in visual-spatial abilities, memory,
2:29:06
Speaker 2: and other aspects of cognition. The exact developmental timetable remains debated,
2:29:12
Speaker 2: and children's dream reports are influenced by language ability and
2:29:16
Speaker 2: by how researchers ask them about their experiences. A young
2:29:20
Speaker 2: child may experience more than they're capable of describing. Still,
2:29:25
Speaker 2: the broad finding is important. Dreaming appears to develop alongside
2:29:29
Speaker 2: the mind that produces it. That makes sense. A brain
2:29:33
Speaker 2: cannot build dream stories using concepts, memories and cognitive abilities
2:29:38
Speaker 2: it has not yet acquired. This is also why the
2:29:41
Speaker 2: extraordinary quantity of active sleep in infancy should not automatically
2:29:45
Speaker 2: be interpreted as evidence that babies spend hours watching extremely
2:29:50
Speaker 2: long internal films. Rapid eye movement-related sleep may serve important
2:29:55
Speaker 2: developmental functions without requiring mature adult-style dream consciousness. During early life,
2:30:02
Speaker 2: the brain is growing rapidly. Neural circuits are being organised.
2:30:06
Speaker 2: Sensory and motor systems are developing. Connections are being strengthened,
2:30:11
Speaker 2: modified and eliminated on an enormous scale. Active sleep may
2:30:15
Speaker 2: participate in some of these developmental processes. Whether subjective dreaming
2:30:20
Speaker 2: accompanies those processes is and what form such experience would take,
2:30:25
Speaker 2: remains much more difficult to establish. Animals and babies therefore
2:30:29
Speaker 2: expose a basic limitation that runs through the entire science
2:30:33
Speaker 2: of dreaming. We can measure sleep beautifully. We can identify
2:30:38
Speaker 2: rapid eye movement states. We can record individual neurons. We
2:30:42
Speaker 2: can watch memories being reactivated. We can observe muscles twitching
2:30:46
Speaker 2: and brain rhythms changing. But eventually, if we want to
2:30:49
Speaker 2: know whether there was an experienced dream We face the
2:30:52
Speaker 2: problem of consciousness. With an adult human, we can at
2:30:55
Speaker 2: least ask. With a rat, a dog, a songbird or
2:30:59
Speaker 2: a newborn baby, that route disappears. The sleeping brain may
2:31:04
Speaker 2: provide strong clues. Evolutionary relationships may make some possibilities more
2:31:09
Speaker 2: plausible than others. But there remains a gap between observing
2:31:13
Speaker 2: what a nervous system does and knowing what the world
2:31:16
Speaker 2: feels like from inside that nervous system. So, when a
2:31:20
Speaker 2: sleeping dog begins moving its paws, it is perfectly reasonable
2:31:24
Speaker 2: to wonder whether somewhere inside that sleeping brain there is
2:31:26
Speaker 2: a field, a path, another dog or something worth chasing.
2:31:32
Speaker 2: Science can tell us that the brain is active. It
2:31:35
Speaker 2: can tell us that mammals share important features of sleep physiology.
2:31:39
Speaker 2: It can even show that sleeping animals reactivate patterns associated
2:31:43
Speaker 2: with waking experience. What it cannot yet do is is
2:31:47
Speaker 2: lean down beside the dog the following morning and ask
2:31:50
Speaker 2: the one question that would settle the matter. So what
2:31:54
Speaker 2: did you dream about? So why do we actually dream?
2:31:58
Speaker 2: After everything science has discovered about sleep, the most accurate
2:32:02
Speaker 2: answer is still slightly unsatisfying. We do not know of
2:32:06
Speaker 2: one demonstrated biological function that fully explains why human beings
2:32:11
Speaker 2: experience dreams. That does not mean science knows nothing about them.
2:32:16
Speaker 2: Far from it. Every night the brain moves through organised
2:32:20
Speaker 2: stages of sleep. Neural networks alter their activity. Memories are reactivated.
2:32:26
Speaker 2: Emotional systems change. Muscles become inhibited. Sensory information from the
2:32:32
Speaker 2: outside world is reduced. And somewhere within all of that activity,
2:32:37
Speaker 2: consciousness can fill with places, people, sounds, fears, arguments, journeys
2:32:42
Speaker 2: and events that never actually happened. A substantial part of
2:32:46
Speaker 2: the night can contain internally generated experience. Then morning arrives,
2:32:52
Speaker 2: and most of it disappears. One of the most important
2:32:55
Speaker 2: distinctions is between sleep and dreaming. Sleep clearly performs many
2:32:59
Speaker 2: biological functions. It affects memory, metabolism, immune activity, emotional regulation,
2:33:06
Speaker 2: brain development, and many other processes. But finding something useful
2:33:11
Speaker 2: happening during sleep does not automatically show that conscious dreams
2:33:15
Speaker 2: exist in order to perform that function. Dreaming may contribute
2:33:20
Speaker 2: to some of those processes, it may accompany them, or
2:33:23
Speaker 2: some dreams may simply be what particular kinds of sleeping
2:33:26
Speaker 2: brain activity feel like from the inside. This distinction has
2:33:31
Speaker 2: followed dream science since Eugene Aserinsky and Nathaniel Kleitman transformed
2:33:35
Speaker 2: the field in 1953. Their discovery of recurring periods of
2:33:40
Speaker 2: rapid eye movements gave researchers a measurable physiological state strongly
2:33:45
Speaker 2: associated with vivid dream reports. William Dement and others then
2:33:50
Speaker 2: helped reveal the repeating architecture of rapid eye movement and
2:33:54
Speaker 2: non-rapid eye movement sleep across the night. Dreams had entered
2:33:58
Speaker 2: the laboratory, but rapid eye movement sleep did not turn
2:34:02
Speaker 2: out to be identical to dreaming. People can report dreams
2:34:06
Speaker 2: after non-rapid eye movement sleep as well. The relationship is powerful,
2:34:11
Speaker 2: but not absolute. John Alan Hobson and Robert McCarley later
2:34:15
Speaker 2: offered the activation synthesis hypothesis. In their account, internally generated
2:34:21
Speaker 2: activity during sleep provides material that higher brain systems attempt
2:34:25
Speaker 2: to organise into an experience. Memories, emotions and imagery become
2:34:30
Speaker 2: combined into a temporary world. This helps explain why dreams
2:34:35
Speaker 2: can be coherent from moment to moment while still containing
2:34:38
Speaker 2: abrupt changes. impossible locations and people who somehow become someone
2:34:43
Speaker 2: else halfway through a conversation. It provides part of an
2:34:47
Speaker 2: answer to how dreams may be constructed. It does not
2:34:51
Speaker 2: necessarily answer why conscious dream experience exists. Memory offers another
2:34:56
Speaker 2: strong candidate. There is excellent evidence that sleep contributes to
2:35:00
Speaker 2: memory consolidation. The sleeping brain reactivates information. Recently learned material
2:35:06
Speaker 2: can be stabilised. New memories can become integrated with older knowledge.
2:35:11
Speaker 2: The hippocampus and wider cortical networks continue exchanging information long
2:35:16
Speaker 2: after the events of the day have ended. And dreams
2:35:19
Speaker 2: frequently borrow from those events. Recent experiences appear. Old memories return.
2:35:26
Speaker 2: People and places from different periods of life become combined.
2:35:31
Speaker 2: Experiments by researchers including Robert Stickgold and Erin Wamsley have
2:35:36
Speaker 2: even found relationships between dreaming about recently learned tasks and
2:35:40
Speaker 2: later improvement. But the careful conclusion remains the same. Sleep
2:35:44
Speaker 2: processes memory. Memories enter dreams. It is still uncertain whether
2:35:50
Speaker 2: experiencing the dream is necessary for the memory processing itself.
2:35:54
Speaker 2: Emotion produces a similar picture. Dreams are often intensely emotional.
2:36:00
Speaker 2: Concerns from waking life can follow us into sleep, sometimes
2:36:04
Speaker 2: transformed almost beyond recognition while preserving the same underlying fear, affection,
2:36:10
Speaker 2: embarrassment or uncertainty. Researchers such as Rosalind Cartwright examined whether
2:36:16
Speaker 2: dreaming might contribute to emotional adaptation. Matthew Walker and Elsvander
2:36:22
Speaker 2: Helm proposed that rapid eye movement sleep could provide unusual
2:36:25
Speaker 2: conditions in which emotional memories are revisited while norepinephrine activity
2:36:30
Speaker 2: is extremely low. Perhaps that helps memories remain while some
2:36:35
Speaker 2: of their emotional intensity changes. It is a compelling possibility.
2:36:40
Speaker 2: But nightmares remind us not to make the story too tidy.
2:36:44
Speaker 2: Dreaming is not automatically therapeutic. A distressing dream can worsen sleep.
2:36:50
Speaker 2: Recurring nightmares can become serious enough to impair waking life.
2:36:55
Speaker 2: Whatever emotional processing occurs during dreaming, it is not simply
2:36:59
Speaker 2: a nightly machine for making unpleasant feelings disappear. Other theories
2:37:04
Speaker 2: go further. Antti Ravonsuo proposed that dreams may simulate threats,
2:37:09
Speaker 2: giving the brain opportunities to rehearse responses to dangerous or
2:37:13
Speaker 2: socially difficult situations. That could help explain why dreams so
2:37:18
Speaker 2: frequently contain pursuit, conflict, escape and loss of control. Eric
2:37:24
Speaker 2: Hall's more recent overfitted brain hypothesis suggests something different. Perhaps
2:37:29
Speaker 2: the strain distortions of dreams introduce useful variability into a brain,
2:37:34
Speaker 2: repeatedly exposed to the regular patterns of waking life. One
2:37:38
Speaker 2: theory emphasises rehearsal, the other emphasises flexibility. Both are interesting.
2:37:45
Speaker 2: Neither has become the accepted explanation for why dreaming exists.
2:37:49
Speaker 2: Even familiar dream themes resist simple interpretation. Falling, being chased,
2:37:55
Speaker 2: missing an examination, arriving late, losing teeth. These experiences occur
2:38:01
Speaker 2: often enough to reveal regularities in the kinds of situation
2:38:04
Speaker 2: human brains construct. But they do not form a universal
2:38:09
Speaker 2: symbolic language. The same dream can arise in people with
2:38:12
Speaker 2: completely different lives for completely different reasons. Common bodies and
2:38:17
Speaker 2: common worries can produce common dreams without requiring a hidden dictionary.
2:38:22
Speaker 2: Lucid dreaming makes the situation stranger still. A sleeping person
2:38:27
Speaker 2: can sometimes realise that the world around them is a
2:38:30
Speaker 2: dream while continuing to experience it. Experiments pioneered by Stephen
2:38:35
Speaker 2: LaBerge allowed lucid dreamers to signal researchers using deliberate eye movements.
2:38:42
Speaker 2: More recent work has even demonstrated limited two-way communication with
2:38:45
Speaker 2: some people, while they remained asleep. The private dream can
2:38:50
Speaker 2: occasionally reach beyond itself, but only slightly. Animals expose that
2:38:55
Speaker 2: limitation even more clearly. Matthew Wilson and Bruce McNaughton showed
2:39:00
Speaker 2: that rats reactivate hippocampal patterns associated with waking exploration during
2:39:05
Speaker 2: later sleep. Sleeping dogs twitch. Birds reactivate patterns connected with
2:39:12
Speaker 2: a learned song. Newborn babies spend enormous amounts of time
2:39:16
Speaker 2: in active sleep resembling rapid eye movement sleep. All of
2:39:20
Speaker 2: this suggests rich processing during sleep, but none of it
2:39:24
Speaker 2: lets us step directly inside another mind. A rat cannot
2:39:28
Speaker 2: describe the maze it may or may not have experienced.
2:39:32
Speaker 2: A baby cannot explain what active sleep felt like. Dream
2:39:36
Speaker 2: science eventually becomes consciousness science. And perhaps that is why
2:39:41
Speaker 2: one final possibility deserves to remain open. Dreams may not
2:39:45
Speaker 2: have one purpose. Different features of dreaming may arise from
2:39:49
Speaker 2: different processes. Memory reactivation may provide some ingredients. Emotional systems
2:39:56
Speaker 2: may provide others. Predictive mechanisms may construct scenes. Spontaneous neural
2:40:01
Speaker 2: activity may introduce unexpected material. Simulation may allow the brain
2:40:06
Speaker 2: to explore possibilities without being constrained by the outside world.
2:40:11
Speaker 2: Some of these processes may be useful. Others may simply
2:40:14
Speaker 2: occur because this is what an active sleeping brain does.
2:40:18
Speaker 2: It is even possible that many important functions belong primarily
2:40:21
Speaker 2: to sleep itself, while the strange stories we experience are
2:40:25
Speaker 2: partly the conscious accompaniment to deeper biological work. After thousands
2:40:30
Speaker 2: of years of interpreting dreams and decades of recording sleeping brains,
2:40:34
Speaker 2: Science can now describe dreaming with extraordinary detail. It knows
2:40:39
Speaker 2: far more about when dreams occur. It knows something about
2:40:43
Speaker 2: which brain systems participate. It can study memory, emotion, eye
2:40:48
Speaker 2: movements and neural activity while the dream is happening. But
2:40:52
Speaker 2: the simplest question remains open. Why should any of those
2:40:55
Speaker 2: processes become an experienced world at all? Perhaps by the
2:40:59
Speaker 2: time you hear these final words, your own waking world
2:41:02
Speaker 2: is already beginning to loosen slightly. Soon enough, the brain
2:41:07
Speaker 2: may begin building somewhere else. A room that does not exist.
2:41:11
Speaker 2: A conversation that never happened. A person you have not
2:41:15
Speaker 2: seen in years. An event that makes perfect sense until morning.
2:41:19
Speaker 2: And whatever dreams ultimately turn out to be for, there
2:41:22
Speaker 2: is a reasonable chance that your sleeping brain will create
2:41:25
Speaker 2: several of them tonight. Most will probably be forgotten by breakfast.
2:41:29
Speaker 2: But for a little while, they will feel completely real.