Maiken Nedergaard

Yes, so they know transmitters or modulators.

So these are noradrenaline, dopamine, serotonin.

They are basically determining when we awake who we are because they're driving emotion, cognition, and desire.

So they have very different functions.

Sometimes they work in parallel, but most of the time they work in different brain regions and at different time points.

So the biggest surprise was that they all synchronize activity and they oscillate.

So they increase about once every minute and fall.

So very, very slow oscillations.

What it comes down to is that during evolution, the brain probably decided to use the neurotransmitters for two different purposes.

One is to decide our awake desire and cognition, and the other is these are the driver of fluid flow when we fall asleep.

So this is very common in evolution, that the same building block is used for multiple purposes, often two or three.

Yes, so this slow wave of activity actually appeared in evolution about 600 million years ago when the very primitive organisms started to have a gut and a vascular system.

And you need to move fluid around in these systems.

These organisms did not even have a heart, but they still have very simple vessels that could move oxygen from one place to another by this very slow oscillation mechanism.

And what probably happened is that evolution decided this is actually a great function to basically constrict and dilate blood vessels about once every minute.

And that is maintained in the human brain.

Now we know this is what moves cerebrospinal fluid around when we sleep.

And we also know why it doesn't happen when we are awake, because these neurotransmitters are not synchronized.

They move a little here, a little there, so there's no concerted movement of fluid flow.

When they're all synchronized when we sleep, we get this highly organized movement of not only blood, but also cerebrospinal fluid, and that is what drives brain clearance.