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- Lasts 24 hours e.g. Sleep/wake cycle. Regulated by external cues e.g. checking watch or meal times
- Mammal's internal biological clock is the suprachiasmatic Nucleus = this regulates the secretion of melatonin in the pineal gland. The SCN is also connected to the retina in the eye which shows the indirect link between exogenous pacemakers such as light and melatonin production from the pineal gland working with the SCN to make a biological rhythm
- Core body temp is another example - low body temp @ 4.30am and highest at 6pm (38 degrees)
- Hormone production - cortisol lowest @ midnight, peaks @ 6am. Affects alertness
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- STUDY: Aschoff and Weber (1965)
- Pp's in bunker w/o natural light = settled into sleep/wake cycle of 25-27 hours on average
- Showed exogenous pacemakers influence the duration of our sleep/wake cycle
- EVALUATION:
- Low ecological validity - lab setting
- Demand characteristics - volunteers
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- STUDY: Michael Siffre
- 6 mnths in a cave w/o external cues = body settled into 24.9 hr rhythm
- EVALUATION:
- Lacks external validity - case study means it is not generalisable to the wider population, individual differences
- Confounding variables - artificial light and temperature
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- BIOLOGICAL APPROACH - behaviour can be explained due to biological structures in the brain or hormonal activity. However, behaviour is more complex than this and less deterministic than biological approaches suggest. Nurture and the enviornment is shown to be important as external cues override our internal biological clock
- REAL WORLD APPLICATIONS - knowledge about circadian rhythms can be applied to drug treatments and can help us know when is best to take them (digestion, heart rate, hormones etc).
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