circadian rhythms

• a circadian rhythm is a biological rhythm that lasts for around 24 hours
• an example of a circadian rhythm is the sleep/wake cycle
• the sleep/wake cycle is governed by an endogenous pacemaker which is called the suprachiasmatic nucleus (SCN)
• light can reset the SCN
• siffre (1975) - free-running circadian rhythm
• siffre spent 6 months in a cave with no natural light, his body clock maintained a cycle of around 25 hours without exogenous zeitgebers

  this suggests that the sleep/wake cycle is free-running but needs entrainment to keep up with the 24 hour day night cycle
• some psychologists have suggested that artificial light can impact measuring the circadian rhythm and that artificial light disrupts this by acting as an exogenous zeitgeber
• czeisler (1999) - study controlling artificial light and found that the circadian rhythm was closer to 24 hours
• aschoff and wever (1976) - group of participants spent 4 weeks in a WW2 bunker, deprived of natural light

  findings: all but one participant (who’s cycle extended to 29 hours) displayed a circadian rhythm between 24-25 hours
• sleep/wake cycle may be slightly longer than 24 hours, but needs an exogenous zeitgeber to entrain it to a 24 hour cycle
• AO3 - helped to improve drug treatments

  lead to the development of chronotherapeutics (how medical treatment can be administered so that it corresponds to a person’s biological rhythms)

  heart attack medicine taken late at night in order to minimise the risk of heart attacks in the morning
• AO3 - research support

  siffre

  aschoff and wever