This article explains the neurobiology of circadian timekeeping, describing what is known about the master pacemaker for circadian rhythmicity, how various biological systems can provide input to the endogenous biological timing, and how the pacemaker can influence the physiology and behavior of the individual. It discusses how the circadian system can adapt to a changing environment by resetting the circadian clock in the face of various inputs, including changes in light, activity, and the sleep-wake cycle. Finally, the article discusses the genetics of circadian time keeping, highlighting what is known about heritable disorders in circadian timing.

Original languageEnglish (US)
Pages (from-to)99-110
Number of pages12
JournalSleep Medicine Clinics
Issue number2
StatePublished - Jun 2009


  • Acetylcholine
  • Advanced Sleep Phase Syndrome
  • Biological rhythms
  • Circadian
  • Glutamate
  • Melatonin
  • Sleep
  • Suprachiasmatic nucleus

ASJC Scopus subject areas

  • Psychiatry and Mental health
  • Neuropsychology and Physiological Psychology
  • Clinical Psychology
  • Clinical Neurology


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