Biological Rhythms

• Biological rhythms


  Periodic physiological fluctuations in the body, such as the rise and fall of hormones and accelerated and decelerated cycles of brain activity, that can influence behaviour.
• Endogenous pacemakers


  Mechanisms within the body that govern the internal, biological bodily rhythms
• Exogenous zeitgebers


  External cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle.
• Circadian Rhythms


  Internally generated patterns of body functions, including hormonal signals, sleep, blood pressure, and temperature regulation, which have approximately a 24-hour cycle and occur even in the absence of normal cues about whether it is day or night
• The sleep/wake cycle


  A daily, naturally occurring 24-hour circadian rhythm of sleep and wake states regulated by a biological clock
• Siffre's cave study


  - Studied effects of his endogenous pacemaker.

  - First time he spent 2 months in the cave, 2nd time 6 months.

  - His free running biological rhythm settled to one just beyond 24 hours (around 25) but did fall asleep and wake up on a regular schedule.
• Strengths of circadian rhythms

  Shift work

  - Night workers engaged in shift work experience a period of reduced concentration around in the morning meaning mistakes and accidents are more likely.

  - Shows that research into the sleep/wake cycle may have real world economic implications in terms of how best to manage worker productivity.

  
  

  Medical treatment

  - Circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels.

  - These rise and fall during the course of a day which has led to the field of chronotherapeutic.

  - For example, aspirin as a treatment for heart attacks is most effective if taken last thing at night.

  -Shows that circadian rhythm research can help increase the effectiveness of drug treatments.
• Limitations of circadian rhythms

  Individual differences

  - Generalisations are difficult to make.

  - Siffre's study is a case study of one person.

  - Difficult to use the research data to discuss anything more than averages, which may be meaningless.
• Infradian rhythms


  Cycle that lasts more than 24 hours

  e.g. menstrual cycle, SAD
• The menstrual cycle


  - 23-36 days

  - Regulated by hormones

  - Oestrogen levels change throughout the month

  - Oestrogen ↑, egg is released, oestrogen ↓ and progesterone ↑
• Stern and McClintock (1998)

  - 29 women with a history of irregular periods.

  - Pheromones collected from 9 women at different stages of their periods using cotton pad under armpit.

  - Other 20 women given pad from 1st day of sample period, then 2nd and so on.

  - 68% of women experienced changes to menstrual cycle bringing them closer to odour donor.
• Seasonal affective disorder


  - A depressive disorder which has a seasonal pattern of onset.

  - Described and diagnosed as a mental disorder in DSM-5.

  - The main symptoms of SAD are persistent low mood alongside a general lack of activity and interest in life.

  
• Strength of Infradian rhythms

  Evolutionary basis

  - May be explained by natural selection.

  - For our distant ancestors, it may have been advantageous for women to menstruate together and become pregnant at the same time.

  - Suggests that synchronisation is an adaptive strategy.
• Limitation of Infradian rhythms

  Methodological limitations

  - Many factors can affect menstrual cycle (stress, diet, exercise).

  - These are confounding variables.

  - May explain why other studies have failed to replicate the findings.

  - Suggests a menstrual synchrony studies are flawed.
• Ultradian rhythms


  Have cycles that occur more than once every 24 hours.
• Stages 1 and 2 of sleep cycle

  light sleep
• Stages 3 and 4 of the sleep cycle

  - Heart rate, blood pressure, and breathing drop to their lowest levels.

  - Replenishing chemical supplies, growth hormones released, immune system repairs.
• Stage 5 of the sleep cycle

  - Rapid eye movement

  - Brainwaves speed up

  - Dreaming occurs

  - Body paralysed

  - Theta-waves
• Strength of ultradian rhythms

  Improved understanding

  - Sleep scientists have observed the sleep wake cycle reduces with age.

  - Knowledge of ultradian rhythms has practical value.
• Limitation of ultradian rhythms

  Individual differences

  - Tucker et al found large differences between participants in terms of the duration of each sleep stage, particularly stages 3 and 4.

  - Makes it difficult to define normal sleep in any meaningful way.