Regulation of circadian physiology and behavior by light in mammals:entrainment and masking

manifestation of circadian rhythms.The modern use of electric lights alters environmental lighting,leading to light exposure at inappropriate times to disturb circadian homeostasis for both human and wildlife.The light“pollution”and voluntary activities such as night shift work and transmeridian travelling have adverse consequences such as mood and metabolic disorders in humans.On the other hand,insufficient light exposure decreases neurotransmission from the locus ceruleus and dorsal raphe,leading to seasonal and nonseasonal affective disorders,while properly timed bright light is beneficial to mood and cognition.Given the critical and complex roles of light in mammalian physiology and behavior,it is essential to understand the underlying mechanisms.In this review,we discuss the neural mechanisms through which light regulates and dysregulates circadian rhythms in mammals.