PHOTOPIC TRANSDUCTION IMPLICATED IN HUMAN CIRCADIAN ENTRAINMENT

Despite the preeminence of light as the synchronizer of the circadian timing system, the phototransductive machinery in mammals which transm its photic information from the retina to the hypothalamic circadian p acemaker remains largely undefined. To determine the class of photopig ments which this phototransductive system uses, we exposed a group (n = 7) of human subjects to red light below the sensitivity threshold of a scotopic (i.e. rhodopsin/rod-based) system, yet of sufficient stren gth to activate a photopic (i.e. cone-based) system. Exposure to this light stimulus was sufficient to reset significantly the human circadi an pacemaker, indicating that the cone pigments which mediate color vi sion can also mediate circadian vision. (C) 1997 Elsevier Science Irel and Ltd.