The science of sleep

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I was reading some interesting facts on sleep and found this:

- Scientists have not been able to explain a 1998 study showing a bright light shone on the backs of human knees can reset the brain's sleep-wake clock.

Does anyone have any ideas why or even how this would happen? Actually what exactly is the brain's sleep-wake clock?

Well they must have hypothesized it would work for some reason to try such a specific thing at all. My first uneducated thought is that there could be biological light receptors there like the one that exists above people's brows that makes them awake and alert. Maybe due to the fact that if bright light makes it to the backs of your knees your body assumes it's highly likely the sun must be out in full force. I wonder if soles of feet have the same receptors.

Could it somehow be related to whatever causes a reflex action in knees whenever a doctor hits it? That signal is coming from the brain.

I think with melatonin as part of some complex cycle, and part of this complex cycle being inhibitory.

Im gonna go out on a limb here.

I think its because like all mammals we are desdended from small burrowing incectovores like hedghogs, shrews, and moles.

These animals tend to be nocturnal even today.

We retain much of the wiring of these animals.

The back of our knees would have been the posterior of the back legs of all of our four footed mammal ancestors.

If the animal is a small burrowing nocternal animal and its sleep clocks tells it that "its day time- so its time for bedy bye" the animal will procede to retreat from the world by burrowing into the ground. But if its back limbs dectect light it knows it must keep on burrowing deeper because its posterior is still exposed. Only when its rear limb light sensors detect only darkness does it know to stop digging because its now safe to sleep.
Actually its a pretty good system because it frees the animal from having to turn around and look over its shoulder with its eyes which is hard to do in a narrow tunnel. It can just keep tunneling.

Our ancestors broke ranks with the other mammals and took to the trees and became diurnal primates early on, 60 million years later we learned to stand upright on two legs and can no longer burrow very well, but we retain these rear limb light sensors. These are still wired into our nervous systems in a way that influences our sleep cycle.

I had a look and found an article published in Science in 2002 that attempted to reproduce the findings. They did not succeed and concluded that the reason for the earlier reports were that they (the 1998 team) failed to shield the patients' eyes from scattered light when illuminating the back of the knees. In short, the back of the knees have no effect but the eyes are far more sensitive than was known when the first trials were made.