Biological rhythms


Suprachiasmatic nucleus (SCN)

  • Stephan and Zucker 1972: Its destruction eliminates the circadian pattern of sleep-waking in rats. Therefore, it has a central role as a endogenous pacemaker or body clock.
  • Melatonin has different effects on the body.
    • induces sleep
    • levels decrease with the onset of light and increase in darkness
    • can be effective treatment for circadian rhythms disrupted through jet lag

What happens when biological rhythms are disrupted?

Our normal pattern: sleep when it is dark, wake it when it is light. This is achieved by the synchrony between body clocks and the onset of light. Disruption can lead to jet lag, depression and fatigue. The latter two were linked to the Chernobyl disaster because workers had to work shifts. Therefore, they were working when their body clocks attempted to impose sleep. This has led to reforms to working hours to improve productivity and the mental wellbeing of workers. --> ECONOMIC IMPACT OF RESEARCH.

Czeisler et al (1982) is an example of research investigating the effects of shift work on employees.

  • In a Utah chemical plant:
    • a backwards shift rotation was used
    • employees worked 7 mornings, then 7 nights
  • Workers experienced lots of stress & health problems
  • After working hours were changed to a forwards shift rotation, workers reported less stress & health problems. Productivity increased.

Siffre (1975): cave study


Michael Siffre spent 179 days in a cave without natural light. This meant that his biological rhythms became free-running. His sleep-waking pattern and physiological functions…


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