In chronobiology, entrainment of a circadian system is the alignment of its own period and phase to the period and phase of an external rhythm, which in this context is called zeitgeber. A common example is the entrainment of endogenous circadian rhythm (which in mammals is generated by the suprachiasmatic nuclei of the hypothalamus) to the light-dark cycle. Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms. ...

References

• Pittendrigh CS (1981) Circadian systems: Entrainment. In Handbook Behavioral Neurobiology, Vol. 4. Biological Rhythms, J. Aschoff, ed. pp. 239-68, University of California Press, New-York.