circadian rhythms

• how long do circadian rhythms last?

  24 hours
• what is an example of circadian rhythms?

  sleep/wake cycle
• circadian rhythm research - Siffre (1975)


  he spent 6 months in a cave in Texas. there were no exogenous zeitgebers. there was no light or time. he had contact with the outside world but was never aware of the time. his sleep/wake cycle was monitored. they found that at the beginning it was erratic but after a while it settled into a 25 hour sleep/wake cycle
• circadian rhythm evaluation - Siffre (1975)


  the data collected is reasonably objective

  it is a case study so generalisation is a bit more difficult

  Wever who's participants spent several months in a bunker found similar findings
• circadian rhythm research - Morgan (1995)

  first they established the presence of circadian rhythms in a group of hamsters by recording their sleep/wake cycle over a period of time. they then removed their SCN. they still ate, slept etc, but their circadian rhythms disappeared. later they transplanted SCN tissue from hamster foetuses, and found that after a few days the circadian rhythms came back. he also transplanted SCN cells from hamsters which had been bred to have longer or shorter circadian rhythms. they found that after transplant, the hamsters took on the rhythms of the donors
• circadian rhythms evaluation - Morgan (1995)

  provided invaluable evidence to suggest that the SCN is the biological clock which controls the sleep/wake cycle.

  carefully controlled scientific procedures were used which have been replicated by other researchers

  however, many critics argue it is not possible to generalise from animals to humans, but their are parts of the brain structure that we cannot control

  some believe that the effects observed were due to trauma from the surgery

  their are some ethical concerns aswell.