Dr. Matt Walker

And sure enough, what we found was that it was REM sleep, rapid eye movement sleep associated with dreaming.

And the greater the amount of REM sleep, the greater the amount of emotional depotentiation, the greater the amount of sort of emotional detox that you got the next day.

And one of the fascinating things that we didn't quite mention in the episode where we described what is sleep, and we described the different stages, including REM, and we spoke about the brain changes.

Something utterly unique happens during REM sleep.

Levels of a brain chemical called noradrenaline are completely shut off.

It is the only time during the 24-hour period when you see the complete cessation of noradrenaline in the brain.

And of course, noradrenaline is associated with many different functions.

You've elegantly described them.

One of the functions is that it's associated with emotional responsivity and the focus and that sort of strong sort of emotional energy.

And people will know we speak about, it has two names, noradrenaline or norepinephrine, same thing, US, UK.

But people, of course, are familiar with the sister chemical in the body called adrenaline.

upstairs in the brain, we can think about noradrenaline.

And during REM sleep, noradrenaline is completely shut off.

This stress-associated neurochemical, it's not only associated with stress, but it's associated with lots of things, but stress included.

No, it's not.

It seems to be specifically within the brain that there is this blockade of noradrenaline and serotonin goes down too.

Whereas another chemical called acetylcholine, which is another neurotransmitter, that ramps up in the brain.

So if there is a brain chemical that seems to be underlying REM sleep or dream sleep, it seems to be acetylcholine.

And in fact, in some parts of the brain,

you can see almost a 30% greater amount of acetylcholine in some brain regions than when we're awake.