Circasemidian rhythm

In chronobiology, a circasemidian rhythm is a physiological arousal cycle that peaks twice in a 24-hour day. It may also be called the semicircadian rhythm. Numerous studies have demonstrated that human circadian rhythms in many measures of performance and physiological activity have a 2-peak daily (circasemidian) pattern.[1] The word, circasemidian, is based upon the Latin words circa ("about"), semi ("half") and dia ("day"). Thus, this is a rhythm that has two cycles per day, and some investigators have referred to it as the semicircadian rhythm. It usually serves to (1) deepen the pre-dawn nadir in body temperature and cognitive performance, (2) create a flat spot during the early afternoon in the daytime increase in body temperature and cognitive performance (the "post-lunch dip"), and (3) heighten the early-evening peak in body temperature and cognitive performance.[2] Broughton was the first to bring this characteristic of human performance to the attention of researchers.[3]

  1. ^ Mitler MM, Carskadon MA, Czeisler CA, Dement WC, Dinges DF, Graeber RC. "Catastrophes, sleep, and public policy: consensus report". Sleep 11:100-109, 1988.
    - Eastman C. "Are separate temperature and activity oscillators necessary to explain the phenomena of human circadian rhythms?" In: Moore-Ede MC, Czeisler CA, editors. Mathematical Models of the Circadian Sleep-Wake Cycle. New York, Raven, 1984. pp. 81–103.
    - US Congress Office of Technology Assessment. Biological Rhythms: Implications for the Worker. Washington DC, US Government Printing Office, 1991.
  2. ^ Miller, J. C. (2006). In Search of Circasemidian Rhythms. Report no. 2006-0074. Brooks City-Base TX: Air Force Research Laboratory.
  3. ^ Broughton RJ. "SCN controlled circadian arousal and the afternoon "nap zone"." Sleep Res Online 1(4):166-178, 1998,
    - Broughton RJ. "Biorhythmic variations in consciousness and psychological functions". Canadian Psychological Reviews 16:217-230, 1975.
    - Broughton RJ. "Chronobiological aspects and models of sleep and napping". In: Dinges DF, Broughton RJ (eds.), Sleep and Alertness: Chronobiological, Behavioral and Medical Aspects of Napping. New York, Raven Press, 71-98, 1989.
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