Behavioral responses to light in mice with dorsal lateral geniculate lesions

Light has rapid direct effects on behavior and physiology that may be disti nguished from its indirect effects that occur via synchronization of the bi ological clock. In nocturnal animals, light at night acutely suppresses the wheel running activity usually observed at that time of day. This is known as masking because light masks the overt expression of the circadian activ ity rhythm. In the present study, we compared the effects of light on wheel running in mice with bilateral electrolytic lesions of the dorsal lateral geniculate nucleus (DLG) to those in sham-operated animals. DLG-lesioned an imals exhibited greater suppression of wheel running in response to bright light than did the controls. but failed to exhibit the increased activity i n response to dim light observed in intact animals, These findings support the view that masking effects of light on behavior comprise two opposing pr ocesses, one that increases activity and is mediated by the classical visua l system. and another that suppresses activity and is mediated by a non ima ge-forming irradiance detection system. (C) 2001 Elsevier Science B.V. All rights reserved.