> Campbell and Murphy found a way to reset this clock with light, but
> the astonishing thing is that the light need not be applied to the
> eyes, anywhere on the skin will do, the back of the knee for
> example. There must be a signal but how the brain knows that light
> is being applied to the back of the knee is a mystery.
The report I heard on NPR didn't say the "signal" was a
mystery. It's via the blood. Evidently the "himo" in the hemoglobin
is molecularly very similar to light sensative stuff that makes plants
green. The "back of the knee" is good because there are lots of blood
vessels close to the surface of the skin and light can be easily
applied there such that the eyes aren't aware of it. Light shined in
the eyes also makes lots of contact with blood so this is why this
sets this clock so well.