David Eagleman

you're actually seeing the visual cortex start responding to that.

And what that means is that this takeover process can start happening really fast because essentially everything in the brain is wired up to everything else.

You know, there's these very long distance connections such that everything has, you know, roadways to get wherever it needs to get.

And so somehow this takeover starts after about an hour.

So what we realized was, given the rotation of the planet,

This causes a real problem for the visual system because you end up in the dark for half the cycle.

And obviously, the thing of interest here is evolutionary time before we had lights, which is just the last nanosecond of evolutionary time where we had lights or even fire.

Most of our history, it's been extremely dark at nighttime, and that means your visual system is disadvantaged during the night.

You can still hear and smell and taste and touch during the night, but you can't see

And so we realized the problem is the visual system needs some way of defending itself against takeover.

And that is what dreams are about.

So every 90 minutes, you've got these very ancient circuits in your midbrain that just blast random activity just into your visual cortex.

That's the only place it's hitting is just primary visual cortex.

And every 90 minutes just blasts random activity in there.

And so dreaming is the brain's way of defending the visual cortex against takeover.

It's essentially a screensaver.

So we published this and we studied 25 different species of primates and looked at how plastic they are.

In other words, humans are extraordinarily adaptable and plastic in their brains.

And that means they're at higher risk of the visual cortex getting taken over.

Whereas other primates,