Biological rhythms: Circadian rhythms + Evaluation

Biological rhythms

Distinct patterns of changes in body activity that conform to cyclical time periods.

Circadian rhythms

A 24 hour cycle (such as sleep-wake cycle and changes in core body temperature).

Supporting Research: Siffre

• Isolated from external factors (light as he stayed underground)

• maintained a regular sleep-wake cycle but it lasted longer than 24 hours

• sleep-wake cycle caused by internal factors but external factors are necessary to fit it to the day/night cycle.

Supporting research: Aschoff and Wever

• participants spent 4 weeks in WW2 bunker, no natural light (isolated from external factors)

• they maintained a regular sleep-wake cycle but it lasted longer than 24 hours except for one participant.

• sleep-wake cycle caused by internal factors but external factors are necessary to fit it to the day/night cycle.

Supporting research: Folkard et al

• 12 people in a cave for 3 weeks

• Researchers sped up the clock so a day lasted 22 hours.

• one participant was able to adjust, clocks as external factors have little impact, therefore supporting internal factors.

Supporting research: Czeisler

• found it's better to change shifts less often (every 21 days rather than 7)

• found it's better to rotate with the clock than against it (staying up later when adjusting to the new shift, get less sleep than more)

Practical applications: Night shift workers

• accidents/mistakes more common during circadian trough (6am)

• health consequences for shift workers

  +Supports internal factors due to negative consequences when external factors try to override internal.

  +suggests circadian rhythms are caused by internal factors

Individual differences:

• free-running sleep-wake cycles can range from 13 to 65 hours

• cycles may change with age (siffre's later cave studies showed a slower circadian rhythm than his earlier ones)

• most individuals are affected by similar external factors but maintain individual regular internal rhythm