Clock Setting; April 1998; Scientific American Magazine; by Hopkin; 3 Page(s)

Organisms from bread molds to bread makers rely on biological clocks that respond to light cues that help them synchronize their activities to the rising and setting of the sun. In humans, this circadian clock controls a variety of physiological processes, including daily rhythms in body temperature, hormone production and sleep itself. Now Scott S. Campbell and Patricia J. Murphy of Cornell University Medical College in White Plains, N. Y., report in Science that they can reset the master circadian clock in humans by shining a light not in the subjects¿ eyes but on the backs of their knees.

"The results are incredibly provocative," says Steve Kay of the Scripps Research Institute in La Jolla, Calif. "And very surprising," he adds, because previous studies in humans suggested that the light signals that entrain the body¿s clock travel to the brain via the retina.