circadian rhythms

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  • Circadian rhythms
    • biological cycles lasting around 24 hours.
    • the sleep/wake cycle is an example of this.
      • this is facilitated by time checks and regular intervals such as meal times.
      • exogenous pacemakers play an important role in the sleep/wake cycle, e.g. light
      • controlled by an endogenous pacemaker
        • this endogenous pacemaker is the superchaismatic nucleus
    • research for the sleep/wake cycle
      • Aschoff and Weber
        • placed participants in a bunker with no natural light and the settled into a sleep/wake cycle between 25 - 27 hours.
        • this suggests that the endogenous pacemaker controls the sleep/wake cycle in the absence of light cues.
      • Siffre
        • spent 6 months in a cave with no time cues. artificial lights came on when he was awake. He settled into a sleep/wake cycle of 25 to 30 hours.
        • after 179 days he thought that only 151 had passed, supporting Aschoff and Weber's findings that endogenous pacemakers exert an influence of circadian rhythm, though the artificial light may have a confounding variable.
    • evaluation for the sleep/wake cycle
      • there are individual differences in the sleep/wake cycle.
        • Duffy et al found that early risers prefer 6am to 10pm and later risers prefer 10am to 1am
        • Aschoff and Weber found in isiolation studies that some participants found it difficult to maintain normal cycles, while others strongly differ.
      • isolation studies have few participants, so makes generalisation problematic.
      • research suggests that endogenous pacemakers do exist and are regulated by exogenous zeitgabers
      • isolating participants from the environment without controlling their behaviour may be insufficient to reveal the activity of the endogenous circadian pacemaker.
        • participants were exposed to high levels of artificial light which may have screw the results by resetting the endogenous pacemaker.


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