Re: Another Clock Found

Geoff Smith (
Fri, 16 Jan 1998 15:41:53 -0800 (PST)

On Fri, 16 Jan 1998, John K Clark wrote:

> of Science, the same one that has the stuff about telomerase and immortal
> human cells, there is another interesting article. Scott Campbell and Patricia
> Murphy found another biological clock, it works at a much higher level than
> the cell and is a part of the brain called the suprachiasmatic nucleus.
> This clock is responsible for our sleep patterns among other things, when it
> gets out of whack we get jet lag and winter depression. 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 authors say the procedure is harmless and easy to do and should soon be
> in common use on airliners.

Also for nightshift workers!

The prevailing wisdom (and the one I know), is that the clock is reset by
something called the retinohypothalamic tract, which is *supposed* to be a
circuit that connects the retina/suprachiasmatic nucleus/hypothalamus/and
pineal gland. What happened to this circuit? Do the auther's propose
that is a fig newton of neuroscientist's imagination? (or an ancillary
mechanism?) This seems very plausible to me... I've always wondered how
moles have their clocks reset by light when they're blind!

This whole blood thing makes a fair amount of sense. It seems to me the
clock must be generated by some chemical negative feedback mechanism,
maybe this mechanism's chemical constituents are altered by the transfer
of high energy electrons from a light-excited hemoglobin molecule?