Dr. David Eagleman

Remember I mentioned earlier that if you go blind, the visual cortex at the back of the brain gets taken over by hearing and by touch and by other things.

And it's no longer visual cortex.

Well, what we realized is that...

Because we live on a planet that rotates into darkness for half the time, the visual cortex, the visual part of your brain, is at a disadvantage.

So what I realized is that the purpose of dreaming is to defend the visual territory from takeover from the other senses.

So every 90 minutes, you've got this very ancient thing in your midbrain that –

shoots random activity into the visual system and only the visual system, only this very tiny part of the visual system.

Every 90 minutes, you just blast random activity in here.

And the reason is you are just defending that territory against takeover.

Now, the reason that all this came together is because our colleagues at Harvard did an experiment where they took normally sighted people and they blindfolded them tightly for 60 minutes.

And it turns out that 60 minutes was sufficient for,

for the visual cortex to start responding to sound and to touch.

You could start seeing that take over happening after 60 minutes.

And that's when we realized, wow, this part of the brain really needs a way of defending itself.

Now, because the brain is a natural storyteller, if you blast random activity in there, it'll put that together in some sort of visual story about what's happening, mostly based on what connections are hot from the day.

But that's why we dream.

If we lived on a different kind of planet that did not rotate into darkness, then we presumably wouldn't dream.

Would we even need to close our eyes?

Not necessarily, yeah.

It may be that in the sleeping state, in the state of deep sleep, the brain is doing particular things like taking out the trash and cleaning some things up.