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Why Do We Dream? · So That's Why

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Jen: Welcome to the So That's Why podcast, where we unpack the
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science behind everyday questions.
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I'm Jen.
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Matt: I'm Chris.
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And I'm Matt.
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Jen: Okay, so tonight while you're lying perfectly still, your brain will
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be building a whole world that's really convincing, and drop you right into it,
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and then clear nearly all of it away before you even wake up enough to notice.
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So why do we dream?
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Matt: This sounds a bit like an episode on the movie Inception to
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me, where my brain creates insane worlds during the night, but I don't
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remember any of it when I wake up.
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Chris: Yep, that's why I don't sleep on planes.
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I don't wanna get incepted.
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Incepted.
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You never know, do you?
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It's fair to say that this really is your brain hard at work.
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I- in fact, in parts of a dream, uh, the brain is as active as when you're
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wide awake, sometimes even more so.
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So this is not a case of the kind of the body relaxing and idling.
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Jen: Which is what we're getting into today, what's happening while you
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dream, what it's quietly doing for you.
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And by the end of it, you'll be able to explain the whole thing
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to someone in one sentence.
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Matt: A sentence, Jen?
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No pressure, but I struggle to summarize a meeting that I was actually awake for.
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Jen: Oh, you'll manage this one, Matt.
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Yeah.
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Matt: All right.
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Jen: Yeah.
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Let's
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Matt: do it.
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Jen: Okay.
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So let's start with how much dreaming we're all doing, because it's
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actually more than people think.
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Chris: It is.
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So most of us have between four and seven separate dreams a night.
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Did you know that?
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Jen: No.
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Chris: And we forget up to 95% of them within minutes of waking up.
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Matt: Wow.
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Between four and seven, so that's five or six.
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Uh, and- Yeah.
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95%. So I mean, I, I have to be honest, every time I dream,
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I rarely do remember them.
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Jen: I know.
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I know.
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And that's the heart of it, and we're saying almost everyone
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dreams every single night.
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I tried keeping a dream journal once, and after a week, all I had was something
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about a train and lots of empty pages.
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Chris: Yeah.
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It's fair to say the, uh, the dreaming bit is the reliable part.
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It's the remembering bit that is less reliable.
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Jen: And here's why the next bit is worth your time.
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Because once you know what the brain's doing during a dream,
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everything else clicks into place.
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Chris: It does.
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So here's what we do know.
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So most vivid dreams happen in the REM sleep phase.
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That's the rapid eye movement, not the shiny happy people- People,
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' Jen: 80s
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Chris: band.
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Or Everybody Hurts.
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I thought you might go with a song there, actually.
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Matt: I'm- I am, I am Superman.
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Jen: That one doesn't come to my mind.
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No.
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Wa-
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Chris: was that something to do with REM, or was that just you?
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I don't know.
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Maybe, yeah.
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I just,
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Matt: it's just one of my- Just what he repeats to himself every day.
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But anyway.
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That's where
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Jen: my
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Matt: dreams are at, Superman.
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Chris: I'll try and kind of pull this back to something resembling the topic.
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Yeah, good
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Matt: luck.
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Chris: Uh, so in REM sleep, the rapid eye movement sleep, uh, this is the stage
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where your eyes flick and about under the lids, and the brain lights right up.
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So the key thing here is that a few regions swing out of their usual balance.
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Matt: Yeah, so go on.
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I mean, I do, I do… I mean, Superman jokes aside, that's the
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dream I have the most, is where I'm falling or flying for a long time.
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Mm.
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Chris: Yeah, well, the, the, the falling one's a great place to start
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actually, 'cause it- it's very common.
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And basically here, the part of the brain that would normally step in and say,
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"Hang on, this wouldn't usually happen.
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I wouldn't u- usually, like, jump down the whole flight of stairs in
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one go," that's the prefrontal cortex, which is the front of your brain that
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handles logic and self-awareness.
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And in that REM phase, it powers right down.
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Matt: That's really interesting.
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So that's- Why I don't question, I guess, the nonsense whilst it's- Mm
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happening whilst I'm dreaming.
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And I'm guessing that's why it all sort of falls apart the second I wake up.
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Jen: Yeah, because the prefrontal cortex becomes more active again at this point,
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bringing back some of the brain's usual systems for reasoning and self-control.
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Meanwhile, the amygdala, which is involved in processing
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emotions, becomes more active too.
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So that combination helps explain why dreams can feel so vivid-
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Mm … and emotionally intense.
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Matt: Which makes sense, doesn't it, I guess?
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'Cause we've all woken up with our hearts pounding, genuinely frightened, uh, by
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something that never really happened.
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Jen: Or actually then really relieved that it didn't.
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Matt: That's true, yeah.
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Um,
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Jen: but the pictures in your dreams themselves come from your visual cortex.
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So that's the part that normally handles what your eyes see.
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Um, and it's firing off on its own with no real input.
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So that's why a dream looks so vivid- Mm … even with your eyes shut.
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Matt: Which is, I guess the images then, they're not just
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old memories playing back.
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My brain's actually generating them fresh in the dark.
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Jen: Mm.
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Chris: Absolutely.
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And feeding the whole thing is the hippocampus, and that's the part of the
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brain that holds your recent memories.
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So it keeps handing the dreams real material.
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Uh, the people, the worries, the odd face from 15 years ago.
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If it's Inception, it's the architecture and everything else.
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And I, I'm definitely, I'm paranoid about Inception.
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Matt: Yeah, yeah, yeah.
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I, I dunno what level I'm at, um-
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Chris: Yeah.
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If anyone's seen it, I've, I've watched it probably 15 times, I still don't
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really understand what's going on.
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Jen: And I think I'm just gonna avoid it totally.
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Yeah.
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I've never seen it.
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You should check
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Chris: it out.
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Recommend.
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It's a, it's a, it's a good movie, but uh-
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Matt: Great soundtrack too.
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Yeah.
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Hans Zimmer.
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Anyway, none of, uh, this is invented from scratch, is it?
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It's my actual life.
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It's kind of shuffled, uh, you know, with the sensible part of
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me not directing it, I suppose.
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Jen: More or less, but there's, there's a raw trigger underneath it too.
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So your brainstem fires off bursts of signals during REM, and the rest of the
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brain scrambles to build a story around them, which is why a dream lurches from
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your kitchen to a beach with no join.
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Matt: Ah, so the plot holes then aren't my fault, not my movie direct gone wrong.
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My brain's improvising over random noise and pretty much
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hoping that I don't notice.
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Chris: Yep.
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That's roughly the idea.
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And, um, there's one more piece.
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So there's a temporary paralysis called muscle atonia, which
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switches on across your body.
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So you stay put instead of physically doing whatever you're
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dreaming, which is probably not
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Jen: a bad
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Matt: yeah, which I, actually, my wife will be very grateful for because I've
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had a lot of those dreams where I am, in fact, the kung fu master, uh, and
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have a lot of fights in my dreams.
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So being still is a good time.
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So prefrontal cortex is down, amygdala is up.
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The hippocampus is feeding it, but the good news is my body is still.
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Jen: Yeah, that is the mechanism in four
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Chris: moves.
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Wa.
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Was that the kung fu move?
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Yeah, yeah.
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That was pretty good.
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Wa.
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Maybe
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Jen: he needs
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Chris: to keep dreaming.
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Yeah.
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Jen: But it even explains the forgetting because the same prefrontal region is
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the part of what bookmarks a memory to keep, and it's turned down so dreams
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barely get flagged or stored as memories.
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Matt: Yes, they vanish, don't they, by morning?
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Not because they're worthless-
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Jen: No, 'cause some dreams are amazing.
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Yeah?
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Matt: Yeah.
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How would, how would… Do, do you log them in your dream diary?
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Jen: No, but sometimes you, like you were saying earlier, when you wake
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up and you're trying to remember a fantastic dream- Oh, yeah … and
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then, but you know it was good.
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Matt: Yeah, well, that's it.
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I mean, but they do, a lot of them do vanish, don't they, because
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you don't actually write them down, uh- Mm … by the morning.
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Chris: And there it is.
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So the one night your brain does its most vivid work, it keeps no receipts.
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I mean, sometimes you can be forgetting a dream as you're trying to remember it.
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You're halfway through the memory and it's gone.
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Yeah.
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Jen: Yeah, yeah.
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Matt: It's inception, I'm telling you.
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Jen: Okay, so that's the how.
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The bigger question is why, and I'll be honest, the, this is still open science,
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so there's no like single settled answer.
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Matt: But I don't believe for one minute, Jen, you've not got a front-runner,
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mainly because we're doing this episode about it and you planned it.
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Jen: Yeah, so we do have a front-runner.
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So the best supported idea is that dreaming is emotional
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pros- memory processing.
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So your brain is sorting through the feelings of the day while you're offline.
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Chris: Yeah, and it's the mechanism that is the most satisfying part, isn't it?
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So in the s- in this state, the brain can hold onto the memory of something that
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upset you while quietly turning down the emotional charge that was attached to it.
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Matt: So you keep what happened, but it stops stinging as much.
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Um, and there's a reason, I guess, we tell people to sleep on it-
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Jen: Mm
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… Matt: um, because this is basically like a literal version, right?
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Mm.
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Jen: Yeah, it is close to literal, and we can back it up.
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So there was a 2024 study published in the journal Scientific Reports, and
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it says that people who dreamed kept their emotionally charged memories.
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They let the neutral everyday stuff fade, and then rated the charged memories
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as less upsetting by the morning.
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Matt: Okay, so the dreaming measurably took the edge off.
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Jen: Mm.
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Matt: Um, hm, that's good.
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That's not just people saying that they felt better.
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I mean, it, if it shows up in the studies, it's got to be true.
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Jen: Yeah, yeah, it did, and there was a nice detail in it, too.
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The more positive someone's dreams were, the more gently they rated the
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previous day's upsetting moments.
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Chris: Yeah, absolutely, and some older work- work from, um, sleep
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researcher Rosalind Cartwright points exactly the same way.
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So in this instance, it was people going through a painful
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breakup who dreamed about it.
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They actually recovered their mood noticeably f-
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faster than those who didn't.
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Matt: So if our brains work it out through the night, do we
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come out the other side quicker?
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Jen: So that's the pattern, though it is fair to say that a lot
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of this still shows a link more than, like, a nailed down cause.
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It's the front runner, but not a closed case.
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Chris: Yeah.
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And while it handles the emotional side, that same overnight sorting, it
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files important memories into long-term storage, and in one study with subjects
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kept out of REM for a few days, they grew far fewer new cells in the hippocampus.
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Matt: That's interesting.
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So block the dreaming, and your memory actually suffers.
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Um, that's more physical, I guess, than I was expecting it to be.
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Jen: Yeah, it is.
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Um, but there's also a smaller idea that dreams let us rehearse tricky
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situations, which fits why being chased or turning up unprepared crop
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up so often the world over in dreams.
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Matt: Yeah.
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So mine, like I said, is the falling flying thing.
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I've no idea what or why, so, you know, I'm taking away w- from this,
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dreaming is my brain processing the day's emotion, filing what matters,
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all while I lie there nice and still.
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Jen: Yeah, that's it, and giving you a chance to prepare for when you are flying.
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Matt: Yeah.
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Yeah.
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I am Superman.
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Jen: Yeah.
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So if someone asks why we dream, you say your brain replays the day
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with the logical brakes off, keeps the memories that count, and eases
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the sting out of them by morning.
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Chris: Yep, and that's a great summary to basically sum up the best
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current science almost word for word.
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Jen: Mm.
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Matt: I feel maybe oddly qualified now.
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I maybe start a career in dreaming- … uh, which is a first.
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Uh, does everyone get the same amount of all this dream thing going on though?
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Chris: No.
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In fact, it shifts a lot with age.
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So babies spend up to half of their time in REM sleep phase, whereas adults
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are nearer a fifth of their time.
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Jen: And the dreams stretch out as the night goes on, too.
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So your first REM stint is short.
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The last one before you wake can run close to an hour, which is why
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the dream you remember is usually the long one that got interrupted.
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Matt: So, so the big finish is always right before the
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alarm wakes me up in a dream.
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Chris: Which is the other factor, how you wake.
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So if you come around gently, and you often catch one, um, you
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get yanked awake, and it's gone before your feet touch the floor.
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Matt: So if I wanna hang on to a dream, um, I hear I've got about
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10 seconds before it evaporates.
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Is that right?
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Jen: Yeah, you do.
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Um, but did you know there's a genuine exception to everybody dreams?
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Um, so after certain rare brain injuries, some people stop dreaming entirely,
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um, even when their REM sleep and their memories carry on completely normally.
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Matt: That's fascinating, isn't it?
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So the dreaming can switch off, uh, on its own without sleeping changing at
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all I mean, that's kind of impressive
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Chris: It is, and it tells us something useful, doesn't it?
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That particular regions actually generate the dream but separate from
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the sleep stage that usually carries it
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Jen: Now, here's where all of this pays off because it tells
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you exactly what a nightmare is
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Chris: Ooh.
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Mm. Yeah, and the dividing line here is simple, that between a bad dream and a
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nightmare, that a nightmare wakes you.
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Um, so whereas a bad dream is unpleasant, you sleep through it, but when it comes
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to a nightmare, it pulls you out of that REM phase with the fear still running
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Matt: Yeah, and it's interesting, if I think about most of the dreams
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that I remember, most of them tilt to being a bit gloomy anyway
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Jen: Yeah, they do, and, you know, roughly two-thirds of dreams
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apparently carry sadness, worry, or anger, and actually only a fifth
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of those are, like, clearly happy.
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So a nightmare isn't some alien event.
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It's that same emotional sorting, but it's just turned up a bit too far
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Matt: Yeah, so this is what we've been talking about, isn't it?
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It's the same process, it's just running maybe a little bit hotter
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Jen: Mm.
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Chris: Yeah, exactly.
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It's a good way of putting it.
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I mean, a nightmare isn't your kind of mind failing.
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It's the, that same system working on something heavy and kind of
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getting stuck partway through
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Jen: Which is why stress is the biggest trigger and why missing sleep does it
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too, because you're skipping off, and the brain packs in extra REM to try
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and catch up, um, a rebound that can make those dreams especially vivid
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Matt: Wow, so a rough fortnight on bad sleep is setting me up-
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for some whoppers
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Chris: Yeah, and for some people, it's, um, it's far more than the odd night.
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Um, so frequent nightmares are common after trauma, affecting
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up to 70% of those living with it
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Jen: Awful
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Matt: Yeah, so for them, it's not, it's not a, a sort of a now and then, is it?
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Uh, so, so it's not an every now and then, it's, it's, it's most nights
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Jen: Mm.
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Chris: That's right, uh, sadly so, and it, d- dare I say it's one of the kind
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of more serious notes for this episode, that if nightmares turn frequent and
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start kind of wearing you down, it is worth talking to your GP, isn't it?
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Because there are treatments out there that genuinely work to overcome this
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Jen: Yeah, and there's a clever one called imagery rehearsal therapy.
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So this is where you rehearse a calmer rewritten ending while you're awake, and
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over time, that new version tends to play out at night instead of the nightmare
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Matt: That's clever
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Jen: Mm
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Matt: So you help the sort of the stuck process finish the job it
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was trying to do, I'm guessing, um, and this only sort of makes sense
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because of what we know it's for
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Jen: Yeah.
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Matt: Which is actually really clever, that you can program your brain to train,
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uh, to change the ending of your dreams.
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Mm. But let me ask you a sideways question that I've always
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wanted to know the answer to.
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Can what we eat actually change our dreams?
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Chris: So, possibly, but I think this is where the evidence
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is a lot thinner, it's fair.
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So, so people, let's be honest, they've blamed everything from spicy food
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to, what, cheese, milk, other dairy products for, for strange dreams.
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But there isn't strong evidence that any particular food
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reliably makes you dream more.
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Jen: There are some interesting clues, though.
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So foods and drinks that affect sleep can indirectly affect dreaming.
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So caffeine, for example, can make it harder to sleep, while alcohol can
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disrupt the normal pattern of REM sleep.
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And because we tend to remember dreams better when we wake during
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or just after REM, changing your sleep can change what you remember.
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Matt: Okay, so it's not the food necessarily, uh, putting a
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particular dream into your head.
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Because if it was, there's another Vegetology supplement right there.
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Um, it might be changing the sleep that the dream happens in.
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Chris: Yeah, exactly.
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And, um, there are a few foods that get talked about because they contain
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compounds involved with sleep chemistry.
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So, uh, tart cherries contain melatonin, for example, and there are
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foods such as nuts, seeds, beans, and whole grains that provide nutrients
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involved in making neurotransmitters.
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But that doesn't mean eating them before you go to bed will
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give you more vivid dreams.
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I think the, the data's all over the place- Mm … and there's theories
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of s- changing how you digest and this, that, and the other, isn't it?
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Jen: Yeah, and that distinction matters, doesn't it?
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Because we have much better evidence that food can influence sleep than we
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do that a particular food can reliably control the content of your dreams.
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So if someone tells you that eating a certain food guarantees bizarre
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dreams, treat that as fun theory, not established neuroscience.
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Matt: Good.
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I was hoping there was a scientifically approved dream menu.
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Chris: Sadly, no.
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So although your midnight snack can still have an effect on the night,
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probably a positive one, um, it just won't help you choose the plot
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of the dreams for the rest of the
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Jen: evening.
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So why do we dream?
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Nobody has the final word yet, but the best evidence says dreaming is your brain
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sorting your day's emotions, keeping the memories that matter, and easing the
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sting out of the hard ones by morning.
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Matt: Yeah, and the forgetting we opened with isn't waste.
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Letting, uh, the ordinary stuff go is part of the brain's job.
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Chris: Yeah, and there's a whole world built and cleared every night,
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kind of quietly keeping you steady.
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Let's be honest, that's not bad for lying down with your eyes shut, is it?
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Jen: So that's why.
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That's it for this week.
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Make sure you hit that subscribe button.
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We're unpacking the science behind everyday questions each
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week, and tell us in the comments what you'd like us to explore.
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Thanks so much for geeking out with us.
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But for now, that's it from me.
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Matt: That's it from me.
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Chris: And that's it from
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Matt: me.
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Jen: Bye for now.
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Matt: Bye.
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Bye-bye.
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Bye.
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Bye.
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Bye.
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Jen: That
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Chris: was wild.