circadian rhythms

• what are circadian rhythms?

  a cycle that takes one day to complete (last 24 hours) e.g. the sleep/wake cycle, core body temperature
• what was michael siffre's aim for his cave study case study?


  to examine the effects of free-running biological rhythms
• what was michael siffre’s cave study procedure?

  on several occasions, siffre spend long periods of time living in dark caves with no external cues (exogenous zeitgebers) to guide his rhythms
• what were the results of michael siffre’s cave study?

  he had a regular sleep/wake cycle

  his circadian rhythm settled down to about 25 hours
• what was the conclusion of michael siffre’s cave study?

  the natural endogenous sleep/wake cycle may be a little longer than 24 hours, but it is entrained by exogenous zeitgebers and associated with 24 hour day (daylight, meal times etc.)
• what did participants in aschoff and wever (1976) WW2 bunker study do?

  spent 4 weeks in a WW2 bunker and were deprived of natural light
• what were the findings of aschoff and wever (1976) WW2 bunker study?

  everyone but one person developed a 25 hour sleep/wake cycle

  one person's sleep/wake cycle extended to 29 hours
• what do the findings of aschoff/wever (1976) WW2 bunker study suggest?

  just like siffre's cave study, the natural endogenous sleep/wake cycle may be a little longer than 24 hours, but it is entrained by exogenous zeitgebers and associated with 24 hour day (daylight, meal times etc.)
• what did participants do in foulkard's (1985) cave study?

  12 participants lived in a dark cave for 3 weeks

  they went to bed when a clock said 11:45, and got up at 7:45

  unknown to the participants, the researchers gradually speeded up the clock

  what seemed to be a 24 hour day was actually a 22 hour day
• what were the findings of foulkard's (1985) cave study?

  only one participant out of 12 comfortably adjusted to the new cycle
• what did the findings foulkard's (1985) cave study suggest?

  we have strong endogenous circadian rhythms that maintain a cycle of 24-25 hours, not easily over-ridden by exogenous zeitgebers
• what is a positive evaluation point of research into circadian rhythms?

  economic implications/IRL application - research has found shift workers experience a lapse in concentration around 6pm so it has managed the health and productivity of workers

  IRL medical application - circadian rhythms coordinate body processes such as heart rate etc. so there are times of day when drugs are better absorbed. guidelines for drug treatment for cancer have been drawn to make treatment more effective
• what is a negative evaluation point for research into circadian rhythms?

  small sample - bunker study had only a small sample of participants and Siffre’s cave study was conducted on one individual, findings lack generalisability and may not represent the wider population
• what is another negative evaluation point for research into circadian rhythms?

  lacks internal validity - artificial light was assumed to have no effect on free-running rhythms so Siffre had a lamp on in his cave study. different research found artificial light could be used to adjust participants' circadian rhythms from 22 to 28 hours, meaning light could've been a confounding variable in Siffre's research and had poor control over extraneous variables