David Eagleman

REM sleep is rapid eye movement sleep. We have this every night, about every 90 minutes, and that's when you dream. So if you wake someone up when their eyes are moving rapidly and you say, hey, what are you thinking about? They'll say, well, I was just riding a camel across a meadow. But if you wake them up at other parts of their sleep, they typically won't have anything going on.

REM sleep is rapid eye movement sleep. We have this every night, about every 90 minutes, and that's when you dream. So if you wake someone up when their eyes are moving rapidly and you say, hey, what are you thinking about? They'll say, well, I was just riding a camel across a meadow. But if you wake them up at other parts of their sleep, they typically won't have anything going on.

REM sleep is rapid eye movement sleep. We have this every night, about every 90 minutes, and that's when you dream. So if you wake someone up when their eyes are moving rapidly and you say, hey, what are you thinking about? They'll say, well, I was just riding a camel across a meadow. But if you wake them up at other parts of their sleep, they typically won't have anything going on.

So that's how we know we dream during REM sleep. But here's the key. My student and I realized that at nighttime, when the planet rotates, We spend half our time in darkness and obviously we're very used to this electricity blessed world, but think about this in historical time over the course of hundreds of millions of years, it's really dark. I mean, half the time you are in blackness.

So that's how we know we dream during REM sleep. But here's the key. My student and I realized that at nighttime, when the planet rotates, We spend half our time in darkness and obviously we're very used to this electricity blessed world, but think about this in historical time over the course of hundreds of millions of years, it's really dark. I mean, half the time you are in blackness.

So that's how we know we dream during REM sleep. But here's the key. My student and I realized that at nighttime, when the planet rotates, We spend half our time in darkness and obviously we're very used to this electricity blessed world, but think about this in historical time over the course of hundreds of millions of years, it's really dark. I mean, half the time you are in blackness.

Now you can still hear and touch and taste and smell in the dark, But the visual system is at a disadvantage whenever the planet rotates into darkness. And so given the rapidity with which other systems can encroach on that, what we realized is it needs a way of defending itself against takeover every single night. And that's what dreams are about.

Now you can still hear and touch and taste and smell in the dark, But the visual system is at a disadvantage whenever the planet rotates into darkness. And so given the rapidity with which other systems can encroach on that, what we realized is it needs a way of defending itself against takeover every single night. And that's what dreams are about.

Now you can still hear and touch and taste and smell in the dark, But the visual system is at a disadvantage whenever the planet rotates into darkness. And so given the rapidity with which other systems can encroach on that, what we realized is it needs a way of defending itself against takeover every single night. And that's what dreams are about.

So what happens is you have these midbrain mechanisms that simply blast random activity into the visual cortex instantly. every 90 minutes during the night. And when you get activity in the visual cortex, you say, oh, I'm seeing things. And because the brain is a storyteller, you can't activate all the stuff without feeling like there's a whole story going on there.

So what happens is you have these midbrain mechanisms that simply blast random activity into the visual cortex instantly. every 90 minutes during the night. And when you get activity in the visual cortex, you say, oh, I'm seeing things. And because the brain is a storyteller, you can't activate all the stuff without feeling like there's a whole story going on there.

So what happens is you have these midbrain mechanisms that simply blast random activity into the visual cortex instantly. every 90 minutes during the night. And when you get activity in the visual cortex, you say, oh, I'm seeing things. And because the brain is a storyteller, you can't activate all the stuff without feeling like there's a whole story going on there.

But the fascinating thing is when you look at the circuitry carefully, it's super specific, much more specific than almost anything else in the brain. It's only hitting the primary visual cortex and nothing else. And so that led us to a completely new theory about dreams. We studied 25 different species of primates, and we looked at the amount of REM sleep they have every night.

But the fascinating thing is when you look at the circuitry carefully, it's super specific, much more specific than almost anything else in the brain. It's only hitting the primary visual cortex and nothing else. And so that led us to a completely new theory about dreams. We studied 25 different species of primates, and we looked at the amount of REM sleep they have every night.

But the fascinating thing is when you look at the circuitry carefully, it's super specific, much more specific than almost anything else in the brain. It's only hitting the primary visual cortex and nothing else. And so that led us to a completely new theory about dreams. We studied 25 different species of primates, and we looked at the amount of REM sleep they have every night.

And we also looked at how plastic they are as a species. It turns out that the amount of dream sleep that a creature has exactly correlates with how plastic they are, which is to say, if your visual system is in danger of getting taken over because your brain is very flexible, then you have to have more dream sleep.

And we also looked at how plastic they are as a species. It turns out that the amount of dream sleep that a creature has exactly correlates with how plastic they are, which is to say, if your visual system is in danger of getting taken over because your brain is very flexible, then you have to have more dream sleep.

And we also looked at how plastic they are as a species. It turns out that the amount of dream sleep that a creature has exactly correlates with how plastic they are, which is to say, if your visual system is in danger of getting taken over because your brain is very flexible, then you have to have more dream sleep.

And by the way, when you look at human infants, they have tons of dream sleep at the beginning when their brains are very plastic. And as they age, the amount of dream sleep goes down.

And by the way, when you look at human infants, they have tons of dream sleep at the beginning when their brains are very plastic. And as they age, the amount of dream sleep goes down.