Biological Rhythms

• Circadian:

  :) RTS Siffre

  > isolated himself in a cave for 6 months - his biological clock was able to be free running and unaffected by exogenous factors, such as clocks and natural light

  > within a few days, he developed a consistent 25 hour cycle - continued to wake and sleep on a regular schedule

  > supports that the sleep-wake cycle is mainly controlled by an endogenous pacemaker (SCN)

  discussion - cycle did adjust to 25 hours, suggesting that exogenous factors are also important
• Circadian:

  :) RTS DeCoursey

  > destroyed the SCN connections in the brains of 30 chipmunks, who were then returned to their natural habitat and observed for 80 days - their sleep-wake cycle disappeared, and a significant proportion were killed by predators - they were awake and vulnerable to attack when they should have been asleep

  > supports importance of endogenous pacemakers, as exogenous zeitgebers alone could not maintain cycle

  discussion - animal bias
• Circadian:

  :( lacks ecological validity

  > research, such as Siffre, are highly controlled and do not reflect how endogenous pacemakers and exogenous zeitgebers interact in real life - they work together, so it makes little sense to separate them for the purpose of research

  > reduces external validity
• Infradian:

  :( RTC Russell

  > a sample of women wore cotton pads under their arms - the pads were then rubbed on the upper lip of 5 sexually inactive women (process was repeated daily for 5 months)

  > 4 out of the 5 women developed menstrual cycles that synchronised to within one day of the donor cycle

  > contradicts that it is mainly governed by endogenous pacemakers - also affected by exogenous zeitgebers

  discussion - field experiment, so low control over extraneous variables
• Infradian:

  :) evolutionary explanation

  > it would have been advantageous for a social group to synchronise pregnancies so that many women would be breastfeeding at the same time - any mother could then take over caring for an orphaned child, to improve chances of survival (adaptive strategy)

  > supports exogenous factors influencing infradian rhythms
• Ultradian:

  :) practical applications

  > helpful in understanding age-related changes in sleep

  > the knowledge that growth hormone is produced during stage 4 has been associated with sleep deficit in old age - research has found older people experience less stage 4 sleep

  > meditation and relaxation techniques have been developed to increase stage 4 in older people to prevent reduced alertness

  > important part of applied psychology
• Ultradian:

  :) scientific methods

  > based on objective and empirical techniques, such as EEGs, to measure brain activity - measure throughout the five stages to identify the length of the rhythm and how many times the rhythm occurs, whilst excluding extraneous variables such as noise and temperature

  > increase internal validity and raises psychology's scientific status
• Ultradian:

  :( lacks ecological validity

  > research conducted in an artificial setting, so the sleep experienced by participants may not reflect their genuine sleep patterns due to unfamiliar surroundings and being attached to electrodes

  > difficult to generalise findings to how ultradian rhythms work in real life

  > lowers external validity