Infradian rhythm

In chronobiology, an infradian rhythm is a rhythm with a period longer than the period of a circadian rhythm, i.e. with a frequency less than one cycle in 28 hours,[1] such as menstruation, breeding, tidal or seasonal rhythms. In contrast, ultradian rhythms have periods shorter than the period of a circadian rhythm. Several infradian rhythms are known to be caused by hormone stimulation or exogenous factors. For example, seasonal depression, an example of an infradian rhythm occurring once a year, can be caused by the systematic lowering of light levels during the winter.[2]

See also

References
  1. Brown, Frederick M. & Graeber, R. Curtis, eds. The Rhythmic Aspects of Behavior. Hillsdale, NJ: Lawrence Erlbaum Associates. 1982, (p.462).
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