Circadian

• What is a circadian rhythm?

  • a type of biological rhythm subject to
  • a 24-hour cycle, which regulates a number of body processes (E.g. sleep/wake cycle and changes in core body temperature)
• SIFFRE'S CAVE STUDY

  • lived in a cave for without any exogenous zeitgebers and measures of time to see the effect on his own biological rhythms
  • He had access to adequate food and drink and resurfaced after 2 months.
  • His natural circadian rhythm settled to 25 hours instead of 24
  • Therefore some processes of identifying when we are hungry/sleepy etc. may be evolutionary.
  • He continued to fall asleep and wake up on a regular schedule.
  • SUGGESTS: we have a natural running cycle which is only a bit over our natural body clock
• What is another study to suggest the importance and existence of circadian rhythms?

  • ASCHOFF AND WEVER (1976)
  • Ppts spent four weeks in a WWII bunker deprived of natural light (EZ)
  • All but one of the participants displayed a circadian rhythm between 24-25 hours
  • One had a sleep-wake cycle extend to 29 hoursSUGGESTS: External cues like light are needed for entrainment
• What do both Siffre's cave study and Aschoff and Wever's bunker study suggest?

  • Both of these studies suggest that the ‘natural’ sleep-wake cycle may be slightly longer than 24 hours
  • but that it is entrained by exogenous zeitgebers associated with our 24-hour day e.g. number of daylight hours, typical mealtimes etc.
• What is counter research to the cave studies? (AO3)

  • FOLKARD ET AL. (1985)
  • Studied 12 people who agreed to live in a dark cave for 3 weeks
  • Retired to bed when the clock said 11.45pm and rising when it said 7.45am
  • Over the course of the study, the researchers gradually sped up the clock (without the participants’ knowledge)
  • A 24-hour day eventually lasted only 22 hours
  • No one could comfortably adjust to the new regime.
  • SUGGESTS: existence of a strong free running circadian rhythm cannot easily be overridden by changes in the external environment
• What is a strength in practical application of circadian rhythm research? (AO3)

  • Knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption (desynchronisation)
  • BOIVIN ET AL 1996 Night workers engaged in shift work experience a period of reduced concentration around 6am (a circadian trough) meaning mistakes/accidents are more likely
  • By reducing night shifts, worker efficiency and productivity can be maximised
• What is another research evidence for practical app? (AO3)

  • KNUTSSON 2003 also found that there is a relationship between shift work and poor health
  • Shift workers are 3x more likely to develop heart disease because of different sleep/wake patterns
  • This results in economic implications to manage worker productivity at the best rate.
• What is a strength of circadian rhythm research in drugs? (AO3)

  • Circadian rhythms co-ordinate the body's basic processes (e.g. heart rate)
  • This effects pharmacokinetics (the action of drugs in the body and their absorption/distribution rate).
  • BARALDO (2008) revealed there are certain peak times during day/night when drugs are most likely to be most effective
  • This has led to the development of guidelines to do with the timing of the drug dosing for a whole range of medications including anticancer/anti-epileptic/respiratory etc.
• What is a limitation of circadian rhythm research sample size? (AO3)

  • Studies of the sleep/wake cycle tend to involve small groups of ppts (e.g. Siffre)
  • The people involved may not be representative of the wider population, decreasing its overall ecological validity to generalise findings
  • In Siffre’s most recent study (1999) he found at 60 his internal clock ticked slower than when he was younger
  • SUGGESTS: even when the same person is involved, there are factors that vary, preventing conclusions to be drawn and generalised.