al living organisms subject to biological rhythm that exert important influence on way body behaves
governed by internal body clock (endogenous pacemakers) + external changes in environment (exogenous zeitgebers)
some rhythms occur many times in a day (ultradian) other longer than a day to complete (infradian) and some much longer (circannual)
circadian rhythms last 24 hours
e.g: sleep/wake cycle + core body temp
Sleep/wake cycle
Feeling drowsy at night and alert in day demonstrated effects of daylight (exogenous zeitgeber)
Governed by internal (endogenous) pacemaker – biological ‘clock’ called suprachiasmatic nucleus – lies just above optic chiasm (provides information from the eye about light), light can reset the SCN
researchers tried to answer what would happen if we don’t have external factors such as light
Siffre’s cave study
Siffre a cave man who spend extended periods of periods underground to study effects on his own biological rhythms
deprived of exposure to sunlight + sound for 2 months in caves of Southern Alps
resurfaced mid-September 1962 believing it was August
performed similar study for 6 months in Texan cave
free-running biological rhythm settled down to one just beyond usual 24hrs - continued to fall asleep + wake in regular schedule
Folkard et al
12 people in dark cave for 3 weeks with a clock (bed = 11:45pm, wake = 7:45am)
researchers secretly speed up clock so 24hours becomes 22 hours
only 1 person able to adjust comfortably
shouldn’t overestimate influence of exogenous zeitgebers
Aschoff + Wever
convinced group of participants to spend 4 weeks in WW2 bunker deprived of natural lightall but 1 participants showed circadian rhythm of 24-25hours (1 showed 29)
all but 1 participants showed circadian rhythm of 24-25hours (1 showed 29)
suggests natural sleep/wake cycle slightly greater than 24 hours but entrained by exogenous zeitgeist's associated with 24-hour day
evaluations
S: understanding consequences of disrupted rhythms: Bovin et al: night workers engaged in shift-work have periods of reduced concentration at 6am (circadian trough) meaning mistakes + accidents more likely + develop heart disease more than those with tropical patterns - real world economic implications HOWEVER use correlation: difficult to establish wether desynchronisation of sleep/wake cycle causes of negotiable effects, Solomon: high divorce rate in shift workers might be due to strian of deprived sleep + other influences (missing out on events) - may not be biological factors
evaluations
S: used to improve medical treatment: rhythms co-ordinate a number of the body’s basic processes that rise and fall during the day, leads to chronotherapeutics (how medical treatment can be administered to correspond to biological rhythms) – e.g. aspirin for heart problems taken at night as heart attacks are more common early in the morning - research can help increase effectiveness of drug treatment
evaluations
S: Wolfson + Carkadon: school day starts couple hours later to accommodate for typical teenage chronotype – hormonal shifts mean getting to sleep becomes more difficult + adolescents tend to be more tired during the morning – benefits for academic + behavioural performance when lessons start later in the day
evaluations
W: generalisations: Aschoff + Wever and Siffre’s research based on small samples, sleep/wake cycles vary from person to person. Czeisler et al: individual differences in cycles vary from 13 to 65 hours + Duffy et al: some people have natural preference for going to bed early and rising early (larks) whereas others are the opposite (owls) + Siffre: observed his own cycle slowed down since he was a young man. —> difficult to use research data to discuss anything more than averages - meaningless