Neural basis and biological function of masking by light in mammals: suppression of melatonin and locomotor activity

Chronobiol Int. 2001 Sep;18(5):737-58. doi: 10.1081/cbi-100107511.


Light influences mammalian circadian rhythms in two different ways: (1) It entrains endogenous oscillators (clocks), which regulate physiology and behavior; and (2) it affects directly and often immediately physiology and behavior (these effects are also referred to as masking). Masking effects of light on pineal melatonin, locomotor activity, and the sleep-wake cycle in mammals and man are reviewed. They seem to represent a universal response in this group. The review reveals that the mechanism of photic inhibition of melatonin is fairly well understood, whereas only little is known about the influence of light on other circadian rhythm outputs, such as locomotor activity.

Publication types

  • Review

MeSH terms

  • Animals
  • Chronobiology Phenomena
  • Circadian Rhythm / physiology*
  • Circadian Rhythm / radiation effects*
  • Geniculate Bodies / physiology
  • Geniculate Bodies / radiation effects
  • Humans
  • Light
  • Melatonin / metabolism
  • Motor Activity / physiology
  • Motor Activity / radiation effects
  • Nervous System Physiological Phenomena*
  • Photoreceptor Cells, Vertebrate / physiology
  • Photoreceptor Cells, Vertebrate / radiation effects
  • Pineal Gland / metabolism
  • Preoptic Area / physiology
  • Preoptic Area / radiation effects
  • Sleep / physiology
  • Sleep / radiation effects
  • Suprachiasmatic Nucleus / physiology
  • Visual Cortex / physiology
  • Visual Cortex / radiation effects


  • Melatonin