Circadian rhythms

• Circadian rhythms= biological rhythms, subject to a 24 hour cycle, which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature.
• Biological rhythm= distinct patterns of changes in the body activity that conform to cyclical time periods. They are influenced by internal body clocks and external changes to the environment.
• Endogenous pacemaker= internal body clocks.
• Exogenous zeitgebers= external changes that influence our internal biological clocks.
• Sleep/wake cycle

  Exogenous zeitgebers= daylight

  Endogenous pacemaker= suprachiasmatic nucleus (SCN) located in hypothalamus provides information from the eye about light.

  SCN regulates activity of pineal gland which releases melatonin.

  Increased light= less melatonin produced

  Decreased light= more melatonin produced.

  Exogenous zeitgebers can reset SCN
• Siffre's cave study

  Siffre spent extended period of time underground to study the effects of his own biological rhythms.

  • Deprived of exposure to natural light and sound for 2 months.
  • His 'free running' biological rhythm settled down to one that was just beyond the usual 24 hours, though he did continue to fall asleep and wake up on a regular schedule.
• Ashoff and Wever study

  A group of participants spent 4 weeks in a WW2 bunker deprived of natural light.

  • All participant apart from one displayed a circadian rhythm between 24-25 hours.
  • Suggests that the 'natural' sleep/wake cycle may be significantly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24-hour day
• Folkard study

  Studies a group of 12 people who agreed to live in a dark cave for 3 weeks, retiring to bed when the clock said 11:45pm and rising at 7:45am.

  • Over the course of the study, the researchers gradually sped up the clock so an apparent 24 hour day eventually lasted only 22 hours.
  • Only 1 participant was able to comfortably adjust to the new regime.
  • Suggests the existence of a strong free-running circadian rhythm that cant be overridden by exogenous zeitgebers.
• Evaluation- shift work

  Strength= understanding of consequences that occur when circadian rhythms are disrupted.

  • Eg: night workers engaged in shift work experience a period of reduced concentration around 6am meaning mistakes and accidents are more likely.
  • Research has also pointed to a relationship between shift work and poor health- X3 more likely to develop heart disease than people who work normal patterns.
  • So research has real world economic implications in terms of managing worker productivity.
• Evaluation- counterpoint

  Studies investigating shift work tend to use correlational methods.

  • This means its difficult to establish whether desynchronization of sleep/wake cycle is actually a cause of negative effects.
  • There may be other factors eg: Solomon concluded that high divorce rates in shift workers might be due to strain of deprived sleep and other influences such as missing out on important family events.
  • Suggest that it may not be biological factors that create consequences associated with shift work.
• Evaluation- medical treatment

  Circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels. These ride and fall during the course of a day which has led to the field of chronotherapeutics= how medical treatment can be administered in a way that corresponds to a persons biological rhythms.

  Eg: aspirin is most effective if taken last thing at night as heart attacks are most likely to happen early in the morning, so timing of taking aspirin matters.

  Show circadian rhythm research can help increase the effectiveness of drug treatments
• Evaluation- individual differences

  Limitation= generalisations are difficult to make.

  • Studies of Aschoff and Wever and Siffre are based on a very small sample of participants.
  • Sleep/wake cycles vary from person to person.
  • Research by Czeisler found individual differences in sleep/wake cycles varying from 13 to 65 hours.
  • Duffy revealed that some people have a natural preference for going to bed r waking up early.
  • Siffre observed that his own sleep/wake cycle has slowed down.
  • Means that it may be difficult to use research data to discuss anything more than averages.