Circadian Rhythms

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  • Circadian Rhythms
    • Stephan and Zucker
      • investigated effects of damage to the SCN
      • rats placed in a laboratory
        • given 12 hours of light followed by 12 hours of dark
        • they're nocturnal
      • they experimental group are operated on to damage their SCN
        • Disrupted their circadian rhythms
          • SCN is a major pacemaker
      • Methodological issues
        • eliminated extraneous variables by damaging other parts of the hypothalamus
          • proved that they didnt influence circadian rhythms
        • difficult surgical procedure
          • only 11 out of 25 rats survived
          • severity of the operation may of affected rats behaviour
        • difficult to generalise rats to humans
          • eg rats are nocturnal
          • low population validity
            • would need to be confirmed by human studies
      • ethical issues
        • cause rats stress and harm
        • killed animals
    • light is the dominant zeitgeber and can reset endogenous  pacemakers
      • Campbell and murphy found that be shining light on the back of someone's knees the circadian rhythm will be altered
    • real life application
      • we live in a world were artificial light is very accessible
        • stevens says they exposure to artificial light disrupts circadian rhythms
    • reductionist
      • in Finland in the winter 6 hours of daylight in summer
      • blind people
        • retina unable to pick up light rays
          • not influenced by exogenous zeitgeber
        • Sack et al found that half of blind people had free running endogenous pacemakers
          • tells us that exogenous zeitgebers are important for the natural synchronising of endogenous pacemakers
        • time givers can be used to synchronise endogenous zeitgebers
      • sunlight can be compromised
        • mechanisms are complex and cannot be diluted to a simple format

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