Dr. Samer Hattar

The period length of the sleep rhythm on average is 24.2 hours.

So you'll be drifting 0.2 hours every day.

out of the solar day if you don't get the sunlight.

So the sunlight adjusts that approximate day to an exact day.

So now your behavior is adjusted to the light, dark environment or the solar day.

It's part of the brain that is not consciously driven.

So you actually do not know when it happens or when it doesn't happen.

And that's what we'll get into when I tell you why light affects your mood and why sometimes people don't know how to deal with light to improve their mood, for example.

So let's do the math.

If you shift out 0.2 hours a day, in five days, you're shifting out one hour.

So you're literally one hour off in your social behavior in five days.

In 10 days, you're two hours off.

And if you're an organism that is living in the wild, shifting out of the right phase of the cycle, you could either miss food or you could become food.

So it's really essential for survival.

I think it's one of the strongest aspects of survival for animals to have the anticipation and the adjustment to the solar cycle.

Yeah, so we knew that in mammals, including us, we are mammals, humans, that the eyes are required for this function.

So if humans are born without eyes or the optic nerves are damaged, humans are not able to adjust to the solar cycle.

So we know that the eyes are required.

In the human retinas, there are two types of photoreceptors.

They are called rods and cones because of their shapes.