circadian rhythms

• biological rhythms -

  • distinct patterns of changes in body activity that conform to cyclical time periods
  • governed by bodys internal biological clocks - endogenous pacemakers
  • and external changes in environment - exogenous zeitgebers
  • ultradian rhythms occur many times during the day
  • infradian rhythms take longer than a day to complete
  • and circadian rhythms
• circadian rhythms -

  • rhythms that last for around 24 hours
  • 2 examples are sleep/wake cycle and core body tempurature
• sleep/ wake cycle -

  • drowsy when night and alert during the day - exogenous zeitgeber is daylight
  • governed by endogenous pacemaker - 'biological clock' the suprachiasmatic nucleus (SCN) - lies just above optic chasm which provides info from the eye about light
  • exogenous zeitgebers (light) can reset the SCN
• Siffre's cave study -

  • spent several extended periods underground to study effects on his own biological rhythms
  • deprived of exposure to natural light and sound - resurfaced mid-september after 2 months believing it to be mid-august
  • decade later performed similar experiment but for 6 months
  • each case his 'free running' biological rhythm settled down to one that was around 25 hours - did continue to fall asleep and wake up on regular schedule
• WW2 bunker cave study: Aschoff and Wever (1976) -

  • participants spent 4 weeks in WW2 bunker deprived of natural light
  • all but one (whose sleep cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours
  • Siffre's and bunker study suggest natural sleep/wake cycle may be slightly longer than 24 hours but its entrained by exogenous zeitgebers associated with our 24 hour day
• cave study on exogenous zeitgebers: Folkard et al (1985) -

  • group of 12 people who lived in a dark cave for 3 weeks
  • retired to bed at 11:45 and rising at 7:45
  • over course of study researchers sped up the clock so apparent 24 day lasted 22 hours
  • only 1 participant was able to comfortably adjust to new regime
  • suggest existence of strong free-running circadian rhythm that cannot be easily overridden by exogenous zeitgebers
• evaluation on circadian rhythms: shift work (strength) -

  • P: provides understanding of adverse consequences that occur when they are disrupted (desynchronisation)
  • E: Boivin et al (1996) night workers in shift work experience a period of reduced concentration around 6am (circadian trough) - mistakes more likely
  • E: Knutsson (2003) relationship between shift work and poor health - shift workers 3x more likely to develop heart disease
  • L: research into sleep/wake cycle may have real-world economic implication of how best to manage worker productivity
• evaluation on circadian rhythms: shift worker counterpoint (limitation) -

  • P: studies investigating effects of shift work tend to use correlational methods
  • E: means its difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects
  • E: Solomon (1993) concluded high divorce rates in shift workers might be due to strain of deprived sleep and other influences
  • L: suggests it may not be biological factors that create the adverse consequences associated with shift work
• evaluation on circadian rhythms: medical treatments (strength) -

  • P: used to improve medical treatments
  • E: circadian rhythms co-ordinate a number of body basic processes (heart rate, digestion, hormone levels) - rise and fall during course of day - led to field go chronotheraputics = how medical treatment can be administered in correspondence to biological rhythms
  • E: Bonten et al (2015) aspirin as a treatment for heart attacks is most effective if taken last thing at night
  • L: circadian rhythm research can help increase effectiveness of drug treatments
• evaluation of circadian rhythms: individual differences (limitation) -

  • P: generalisations are difficult to make
  • E: Aschoff and Wever + Siffre's research based on very small sample - sleep/wake cycles may vary widely from person to person
  • E: Czeisler et al (1999) found individual differences in sleep/wake cycles varying from 13-65 hours - Duffy et al (2001) individual natural preference for early bed, early rising (larks) or opposite (owls)
  • L: means its difficult to use the research data to discuss anything more than averages which may be meaningless