Circadian Rhythms

Question 1

What is a circadian rhythm?

Answer 1

Any cycle that lasts about 24 hours, optimise an organism’s bodily functions and behaviour to best meet the varying demands of the day and night cycle

Question 2

What are the features of the sleep wake cycle?

Answer 2

• Light and dark provide signals about when we should be awake and asleep
• Controlled by homeostasis - controls need to sleep
• The effect of exogeneous zeitgeber has important effect on when we feel drowsy and awake

Question 3

What was Siffre’s cave study (1962)

Answer 3

• Lived underground for 63 days
• Wanted to prepare an ecological expedition but decided to live without a clock underground
• Took two tests - took pulse, counted from 1-120 for 2 minutes but he psychologically experienced 5 minutes as if they were 2

Question 4

What did Siffre’s study show?

Answer 4

Humans are a biological clock, when we are not exposed to light we forget and do not have a sense of time - biological clock allowed to free run

Question 5

How does the release of melatonin affect the sleep wake cycle?

Answer 5

• Peaks during dark hours
• Encourages feelings of sleep by activating synapses in the brain
• Dark = more, light = less

Question 6

How does body temperature indicate the sleep wake cycle?

Answer 6

• Lowest at 4am, highest at 6pm
  -Sleep occurs when temperature drops
• Temperature rises in last few hours of sleep which causes people to feel alert in the morning
• Small drops between 2pm and 4pm which make people feel sleepy

Question 7

What was Aschoff and Wever’s study (1976) on the sleep wake cycle and their findings?

Answer 7

Procedure:
- 4 weeks
- Underground WW2 bunker
- Had artificial light but no natural, and complete lack of environmental and social cues
Findings:
- Participants settled into sleep wake cycle of 24-25 hours, but some 29 hours

Question 8

What was Folkard et al’s study (1985) on the sleep wake cycle?

Answer 8

Procedure:
- 3 weeks
- Dark cave
- Group of 12, sleep when clock said 11:45pm and wake when said 7:45am
- But researchers sped up the clock so the day was 22 hours
Findings:
- Only 1 adjusted
- Suggests existence of strong running circadian rhythm cannot be easily overridden by changes to external environment