Dr. Matt Walker

And REM sleep is the...

Depending on your definition, and we'll probably come to this in later episodes, it's the principal stage in which we dream.

But if your definition is quite loose, which is any reported mental activity when I wake you up or when you wake up, then it turns out that we dream in almost every stage of sleep.

But I'll describe REM sleep from here on in as perhaps dream sleep, and I'll make that faux pas.

So you've got these two types of sleep, non-REM and REM sleep.

they will then play out in this beautiful battle for brain domination throughout the night.

And that cerebral war is going to be won and lost on average for the average adult every 90 minutes.

And then it's going to be replayed every 90 minutes.

And that creates the standard cycling architecture of sleep.

So whoever is listening to this, when your head hits the pillow tonight, what will happen?

You'll start to go down into the light stages of non-REM, then you'll go down into the deeper stages of non-REM sleep, and you'll stay there.

And after about 45, 50, 60 minutes, you'll start to rise back up again, and then you'll pop up and you'll have a short REM sleep period.

And then back down you go again, down into non-REM sleep and up into REM sleep.

And as I said, you cycle through that on average about 90 minutes, but I'll come back to that.

What's interesting, however, is...

The ratio of non-REM to REM within your 90-minute cycle is not stable.

And what I mean is, as you move across the night, the domination of those two types of sleep within the 90-minute cycle changes such that in the first half of the night, the majority of those 90-minute cycles are comprised of lots of deep non-REM sleep, but very little REM sleep.

But as we push through to the second half of the night, now that ratio balance, that seesaw balance shifts over and instead we have much more rapid eye movement sleep and very little deep sleep.

So when people think about, okay, I just go to sleep, I lose consciousness, my brain is still, firstly,

Nothing further from the truth could be the case in terms of your sleep.