circadian rhythms

• sleep/wake cycle:

  • circadian rythym
  • governed by daylight + internal biological clock (suprachiasmatic nucleus)
  • located above the optic nerve - provides info from eyes about light
• Siffre's cave study:

  • spent extended periods of time in cave - deprived of exposure to natural light
  • free running biological rhythm settled to around 25 hours - did sleep/wake on a regular schedule
• aschoff and wever:

  • spent 4 weeks in WW2 bunker - deprived of natural light
  • all but 1 (29 hours) displayed rhythms of 24-25 hours
  • suggest natural cycle may be >24 hours but its entrained by exogenous zeitgebers
• folkhard et al:

  • 12 participants, 3 weeks
  • researcher secretly sped up time - 24 hour day lasted 22
  • 1 participant comfortably adjusted
• core body temperature:

  • fluctuates throughout the day (36 to 38)
  • rises in day, falls at night, falls in afternoon
  • cooler you are = sip in cognitive performance
• EVALUATION: shift work (adverse consequences when rhythm disrupted)

  • night shift workers - experience lower concentration at 6am (mistakes/accidents)
  • research for link between shift work + poor health - 3x more likely to develop heart disease
  • sleep/wake research may have real world economic implications - increase productivity
• EVALUATION: improves medical treatments

  • rhythms coordinate basic processes e.g hormone levels - rise and fall in day leading to field of chronotherapeutic
  • aspirin for heart attacks most effective taken at night - heart attack more likely in morning (timing matters)
  • rhythms can improve effectiveness of drug treatments
• EVALUATION: individual differences (cant generalise)

  • small samples e.g Siffre - cycles vary from person to person + zeistler et al found evidence of variation of 13-65h hours
  • duffy et al - people have natural preference for going to bed early + rising early (larks) = opposite (owls)
  • difficult to use research data to draw conclusions, limits external validity