Dr. Matt Walker

So from the moment that you and I woke up this morning and everyone listening, a chemical has been building up in your brain.

That chemical is called adenosine.

And the more of it that builds up, the sleepier and sleepier you will feel.

And after about 16 or so hours of being awake, there is enough of that sleepiness chemical, that adenosine sleep pressure.

And by the way, it is a chemical pressure.

It's not a mechanical pressure.

You don't have to worry that your head's going to explode if you go longer than 16 hours awake.

that sleep pressure is going to start weighing down on your shoulders.

And you can sense that feeling where you start to think, you're watching television, you're starting to go down sort of the hill and you think, I should go to bed, I'm tired now.

That's because of one of two things is happening.

Firstly, you're getting to that peak crescendo of adenosine where it's just getting so powerful that it's knocking you over and you're ready for sleep.

Usually when you are in synchrony with all of your biology, these two forces, your circadian rhythm that goes up and down every 24 hours and your sleep pressure align in this beautiful sort of Fred Astaire, Ginger Rogers dance partnership.

and they're in harmony.

The strange thing is that they know nothing about each other and they don't care about each other.

One does not influence the other.

They are completely two independent things.

But let me run it out in the normal circumstance, and then I'll describe to you a good example of how I can separate those two and show you that they're truly independent.

So normally when we're in a sort of stable rhythm of sleep-wake activity, we're awake during the day, we've got this awesome upswing of our circadian rhythm.

And then in the evening, let's just take you for example, as you're getting into that sort of 8, 9 p.m.

region, your circadian rhythm has finished its peak many hours ago and it's now starting to descend down and you're getting onto the steep phase of its peak.