Circadian rhythms AQA A LEVEL PSYCHOLOGY BIOPSYCHOLOGY

Circadian rhythms.pptx

1. Biological rhythms: Circadian rhythms

2. Biological rhythms All living organisms are subject to biological rhythms. Biological rhythms are governed by: Endogenous pacemakers – internal biological clocks Exogenous zeitgebers – external environmental factors Circadian rhythms last for approximately 24 hours e.g. the sleep/wake cycle and core body temperature.

3. The sleep/wake cycle Daylight is an important exogenous zeitgeber on the sleep/wake cycle. Endogenous pacemakers also control the sleep/wake cycle. The suprachiasmatic nucleus or SCN is located just above the optic chasm. The SCN detects light and tells the pineal gland to stop producing the sleep hormone melatonin . Exogenous zeitgebers reset or entrain the SCN keeping it to a 24 hour cycle.

4. Siffre’s cave study Siffre spent several extended periods underground to study the sleep/wake cycle. Deprived on the exogenous zeitgeber of natural light, he emerged after two-months in a cave in the Southern Alps in mid-September 1962 believing it was August. 10 years later he repeated the exercise but for 6 months in a Texan cave. In both cases his free-running biological rhythm settled to around 25 hours.

5. Other research Aschoff and Weaver asked participants to spend four weeks in a WWII bunker deprived of natural light. All but one displayed a circadian rhythm of 24-25 hours. One extended to 29 hours. This suggests that the natural sleep/wake cycle is slightly longer than 24 hours but is entrained with exogenous zeitgebers.

6. Evaluation: Practical applications Research into the sleep/wake cycle has important practical applications. Shift workers experience a period of reduced concentration around 6.00 am meaning mistakes are more likely. Shift worker are also 3 times more likely to develop heart disease. This shows research into the sleep/wake cycle has important real-world economic implications in terms of managing productivity.

7. Evaluation: Practical applications II Furthermore, research into circadian rhythms has been used to improve medical treatments. Chronotherapeutics studies how medical treatment can be administered in a way to correspond to biological rhythms. E.g. aspirin used to reduce the risk of heart attack is most effective taken at night as heart attacks are more likely to happen in the morning. This shows that research into circadian rhythms can increase the effectiveness of drug therapies.

8. Evaluation: Individual differences A limitation of research into circadian rhythms is there are individual differences. Studies are based on small samples and the sleep/wake cycle varies between people. In Aschoff and Weaver’s study one individual had a cycle of 29 hours. Siffre observed how his cycle slowed with age. Some people are larks and others are owls. This means that it is difficult to generalise research into the sleep/wake cycle.

9. Evaluation: Methodological issues A weakness is there are methodological issues with research into circadian rhythms. Siffre was exposed to aritificial light which may have acted as an exogenous zeitgeber. Other studies which control for artificial light suggest the sleep/wake cycle is nearer 24 hours. Therefore, research may lack validity which questions conclusions about the body’s internal clock.

10. Exam questions Julia complains that her baby is sleeping all day and keeping her awake all night. Using your knowledge of research into exogenous zeitgebers, discuss what Julia could do to encourage her baby to sleep more at night. ( 8 marks)