CIRCADIAN RHYTHMS

• Biological rhythms


  Distinct patterns of changes in body activity that conform to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers)
• Endogenous pacemakers


  Internal body clocks
• Exogenous zeitgebers


  External changes to the environment
• Circadian rhythms


  A type of biological clock that operates along a 24-hour cycle. This regulates several bodily processes such as the sleep-wake cycle and core body temperature.
• The sleep wake cycle

  The sleep-wake cycle dictates when humans should be awake and asleep, controlled by exogenous zeitgebers such as light and dark. It is also governed by an internal body clock (endogenous pacemaker) called the SCN located in the hypothalamus.
• SCN


  The SCN receives information about light and the exogenous zeitgebers can reset the SCN - sends a message to the pinal gland to secrete/reduce melatonin based on light levels.
• Siffre's cave study - AIM


  His aim was to investigate the influence of an absence of external cues on circadian rhythms. He lived in a cave away from any sources of natural light and ate and slept depending on when he felt he needed to.
• Siffre's cave study - RESULTS


  He resurfaced in mid-September and believed it to be mid-August. His biological rhythm was 25 hours but did maintain a regular schedule.
• Siffre's cave study - CONCLUSION

  This suggests that the biological clock ran at a natural rate and circadian rhythms persist despite the absence of exogneous zeitgebers, but we do need the entrainment of exogenous zeitgebers to keep to the 24-hour cycle.
• Folkhard et al


  This study shows the influence of environmental cues should not be overestimated. 12 people stayed in a cave for three weeks, going to bed and waking up at a set time as shown by a clock. As the study continued the researchers sped up the clock so the day only lasted 22 hours. Only one of the participants was able to adjust, suggesting the free running biological clock can override some external changes in the environment.
• Core body temperature (1)

  Our lowest body temperature is 36 degrees at 4.30am and our highest is 38 degrees at 6pm. Our mental abilities are affected, the warmer we are internally the better our cognitive performance.
• Core body temperature (2)


  Sleep typically occurs when the core body temperature starts to drop and the body temperature starts to rise at the end of a sleep cycle promoting feelings of alertness in the morning.

  GUPTA (1991) - IQ performance improved when assessed at 7pm as opposed to 2pm and 9am
• Strengths - AO3


  ✅Practical application to shift work – research shows there is a period of reduced concentration around 6am, therefore more mistakes likely to occur – informs employers about working hours and what would be more beneficial and less harmful to their work. 

  ✅Practical application to drug treatments – aspirin is most effective last thing at night – by understanding circadian rhythms, it can help determine best time for drug treatment – peak times when drugs are most effective 
• Limitations - AO3

  ❌Small samples and individual differences – Siffre's study was only one person – cannot be generalised to the wider population as it is not a representative sample size – no population validity and lack of control over individual differences. 

  ❌Poor control in studies – Siffre turned a lamp on every time he woke up which remained on until he went to bed – an assumption that artificial light would have no impact but may help keep the circadian rhythm as normal – affects validity of study