8. Biological Rhythms - Circadian Rhythms

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    1. Biological Rhythms - Circadian Rhythms

    Biological Rhythms - changes in body activity that conform to cyclical time periods.
    • BR influenced by endogenous pacemakers (internal body clocks, regulate BRs) + exogenous zeitgebers (external cues from environment affecting BRs).
  • 1a. Biological Rhythms - Circadian Rhythms
    Circadian Rhythms:
    • type of BR, in which pattern of behaviour occurs every 24hrs; reset by environmental light levels.
    • regulates many processes like sleep/wake cycle + body temp changes.
  • 2. Biological Rhythms - Circadian Rhythms
    The Sleep/Wake Cycle:
    • light/darkness main exogenous zeitgebers determining when need sleep/wake.
    • circadian rhythms dip/rise at certain times of day; strongest sleep-drive occurring in ‘circadian troughs’ (11am-2am).
  • 2a. Biological Rhythms - Circadian Rhythms
    Sleep/Wake Cycle - Siffre’s (1962) Cave Study:
    • investigate power of ‘free-running‘ CR, entered cave w/ no exogenous zeitgebers to guid CR.
    • ate + slept/woke when felt needed to.
    • documented s/w cycle + found naturally settled at 25hrs.
    • emerged at 17th Sept (‘62) believing it was Aug.
    • ‘free-running’ BR settled down to 1 that was beyond 24hrs, but did continue s/w regularly.
  • 2b. Biological Rhythms - Circadian Rhythms
    Aschoff + Weaver (1976):
    • sent participants into WW2 bunker for 4wks.
    • all but 1 p. showed CR rhythms between 24-25hrs.
    • natural free-running s/w cycle longer than 24hrs, but governed by exogenous zeitgebers, associated w/ 24hrs.
    • support Siffre (1962).
  • Biological Rhythms - Circadian Rhythms (Evaluation)
    Strength (CRs)
    P - knowledge of CRs = better understanding of adverse consequences that can occur as result of disruption.
    E - e.g. night workers engaged in shift work + experience period of reduced concentration at around 6am = mistakes more likely.
    E - suggested relationship between shift work + poor health; 3x more likely develop heart disease.
    L - real-life application in advice.
  • Biological Rhythms - Circadian Rhythms (Evaluation)
    Limitation (CRs):
    P - studies of S/W cycle involve small groups or individuals.
    E - people involved not be representative of wider pop; limits meaningful generalisations.
    E - Siffre, another study, observed at 60y/o, internal clock ticked slower than when he was young.
    L - low application + generalisability.
  • Biological Rhythms - Circadian Rhythms (Evaluation)
    Limitation (CRs):
    P - participants in studies deprived natural light, still had artificial light.
    E - Siffre turned lamp every time woke up, remained on until went bed.
    E - assumed by him (others) artificial light have no effect on free-running BRs.
    L - low reliability bc internal validity called into question.