Functional absence of extraocular photoreception in hamster circadian rhythm entrainment.

The mammalian circadian pacemaker is entrainable by light via the retina. The putative role of extraocular light perception was investigated in blinded hamsters. These animals were shaved and exposed to a light-emitting pad for either 30 min or 3 h. The absence of any phase-shifting effects on wheel running activity rhythms indicates that extraocular light perception plays no functional role in photic entrainment of the circadian pacemaker in the hamster. Copyright 1999 Elsevier Science B.V.