Dr. David Berson

If they've got retinal blindness,

is insomnia and- Because the brain's awake in the middle of the night.

Exactly.

They're not synchronized.

Their clock is there, but they're drifting out of phase because their clock's only good to 24.2 hours or 23.8 hours.

Little by little, they're drifting.

So you need a synchronization signal because otherwise you have nothing to actually confirm when the rising and the setting of the sun is.

That's what you're trying to synchronize yourself to.

Right.

So the first thing to say is that, as you said, the clock is all over the place.

Most of the tissues in your body have clocks.

The role of the central pacemaker for the circadian system is to coordinate all of these.

There's a little nucleus, a little collection of nerve cells in your brain.

It's called the suprachiasmatic nucleus, the SCN.

And it is sitting in a funny place for the rest of the structures in the nervous system that get direct retinal input.

It's sitting in the hypothalamus, which you can think about as sort of the great coordinator of

drives and- The source of all our pleasures and all our problems.

Yes, it really is.

But it's sort of deep in your brain, things that drive you to do things.

If you're freezing cold, you put on a coat, you shiver, all these things are coordinated by the hypothalamus.