EXTRAOCULAR CIRCADIAN PHOTOTRANSDUCTION IN HUMANS

Physiological and behavioral rhythms are governed by an endogenous cir cadian clock. The response of the human circadian clock to extraocular light exposure was monitored by measurement of body temperature and m elatonin concentrations throughout the circadian cycle before and afte r light pulses presented to the popliteal region (behind the knee). A systematic relation was found between the timing of the light pulse an d the magnitude and direction of phase shifts, resulting in the genera tion of a phase response curve. These findings challenge the belief th at mammals are incapable of extraretinal circadian phototransduction a nd have implications for the development of more effective treatments for sleep and circadian rhythm disorders.