Circadian Rhythms

• Circadian rhythms are biological rhythms that last for around 24 hours e.g. sleep-wake cycle, core body temperature
• Siffre's cavy study investigated the sleep-wake cycle as he spent 6 months in a cave in the Alps deprived of exposure to natural light and sound
• Siffre resurfaced in mid-september believing it to be mid-august
• Siffre's free-running circadian rhythms settled to about 25 hours
• The sleep-wake cycle is governed by the SCN and light
• The sleep-wake cycle has two dips between 2-4 AM and 1-3 PM
• In the absence of exogenous zeitgebers the free-running circadian rhythm would last 25 hours
• Core Body Temperature varies by about 2 degrees every day
• Core body temperature is lowest at 4AM (36) and highest at 6PM (38)
• Warmer body temperature increases cognitive performance
• Folkard et.al investigated the sleep-wake cycle using 12 participants who spent 3 weeks in a cave whilst researchers gradually sped up the clock
• Folkard et.al found that the majority of participants were unable to comfortably adjust
• Shift work demonstrates circadian rhythms as night workers have been shown to experience a period of reduced concentration at around 6AM which increases the likelihood of mistakes
• There has to been shown to be a relationship between shift work and poor health
• Knuttson found that shift-workers are 3 times more likely to develop heart disease
• Research into medical treatment supports circadian rhythms e.g. Chronotherapeutics
• Chronotherapeutics is when medical treatments can be administered in a way that corresponds to someone's biological rhythms
• An example of chronotherapeutics is that aspirin is more effective for heart attacks when taken late at night
• There are individual differences in circadian rhythms as cycles can vary from 13-65 hours
• Jeane Duffy et.al supports individual differences as she found that some paeople are 'larks' or 'owls' due to natural preferences