Biological rhythms

• What is a biological rhythm?

  A distinct pattern of change in body activity that conforms to cyclical time periods. They are influenced by internal body clocks and external changes to the environment.
• What is a circadian rhythm?

  Biological rhythms that are subject to a 24 hour cycle

  eg. the sleep wake cycle or body temperature
• What is the sleep/wake cycle?

  The external factor of daylight helps control when we feel awake / asleep, and this triggers the biological ‘clock’ of the suprachiasmatic nucleus which then coordinates the activity of the whole circadian system
• What is the body temperature cycle?

  Body temperature is at it’s lowest in the early hours of the morning- 36 degrees at 4.30am.

  It is at it’s highest in the early evening- 38 degrees at 6pm.

  As temperature drops, sleep occurs.
• Who provided research support for biological rhythms?

  Siffre’s cave study

  Aschoff and Wever
• What did Siffre do?

  He spend several periods underground- 2 months in France and 6 months in Texas - to study the effect on his own biological rhythm. He was deprived of natural light and sound, but had food and water. Both times he found his ‘free running’ biological rhythm extended to around 25 hours, but he still continued to wake and sleep at regular times.
• What did Aschoff and Wever do?

  Encouraged a group of participants to spend 4 weeks in a cave, and all but one of their circadian rhythms increased between 24 and 25 hours
• What evidence did Folkard dispute with?

  His study followed 12 people who lived in a cave for 3 weeks, following a clock which was manipulated by researchers so the day eventually was only 22 hours.

  Only 1 participant comfortably adjusted to this, showing that external changes cannot override circadian rhythms.
• What is a real world strength of biological rhythms?

  It explains shift work and so has real world economic implications of how to best manage worker productivity. Night workers experience reduced concentration at around 6 in the morning, meaning accidents are more likely. Shift workers are also 3 times more likely to develop heart disease than those who work regular patterns (Knutssan), showing the adverse affects of interrupting the sleep/wake cycle.
• What is an issue with real world application of the ideas?

  Correlational methods means it is hard to establish cause and effect of the sleep/wake cycle to negative effects, as other factors may be at play.

  Solomon concluded that high divorce rates in shift workers was due to the strain of deprived sleep and missing out on family events, rather than biological factors.
• What is another strength of the theory?

  Application to medical treatment- as circadian rhythms coordinate several basic bodily processes (heart rate, digestion), this has led to developing how treatments can be administered in a way which correlates to biological rhythms (chronotherapeutics), such as aspirin being the most effective for heart attacks when taken last thing at night.
• What is an issue with this theory?

  Individual differences means generalisations are hard to make, as small sample sizes are not representative and research shows wide variations.

  Czeisler found the cycle varies from 13-65 hours.

  Duffy found people have natural preferences for sleeping and waking.

  Therefore, a holistic approach may be better to form wider generalisations.