Psya3 - Biological Rhythms and Sleep, Relationships and Aggression Notes

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Biological rhythms and Sleep
Circadian rhythms
Those which complete a cycle in a 24 hour period such as the sleep-wake cycle, heart rate or metabolism.
Temporal isolation studies demonstrate that the cycle persists despite the absence of light. Siffre spent long
periods in a cave with no exogenous zeitgebers. Found that his sleep-wake cycle generally adjusted to a 24 hour
cycle yet sometimes changed. This study is also supported by Aschoff and Wever who placed participants in an
underground bunker, the participants cycle was 24-25 hours.
Cycles can be entrained to some extent by external cues. Folkard et al reduced participants circadian rhythms using
a quickening clock but at 22 hours the participants own rhythms took over again showing a limit for control of
internal rhythms.
Our core body temperature is lowest at about 4.30AM (36°c) & highest at about 6.00PM (38°c). Folkard et al tested
memory recalls in children and the results were better when temperature was higher.
Post-lunch dip: tiredness in the afternoon appears to be due to the effects of having eaten, but it also occurs even if
you don't eat due to a circadian temperature rhythm.
Hormones such as cortisol levels are lowest at midnight, and peak at about 6AM ­ high levels mean increased
alertness. Furthermore melatonin and growth hormone levels peak at night.
Miles et al: blind people show the same pattern as sighted people therefore it must be due to an internal
1. Individual differences: there are individual differences in the variation of cycle length. Ceizler stated that
cycle length varies from 13 to 65 hours. This variation of cycle time shows a huge gap in between therefore
individual differences needs to be taken into account.
2. Biological and deterministic approach: all these explanations suggest our sleep-wake patterns are fixed.
This may be misleading as we have the power to override such processes.
3. Research methods: case studies lack population validity as they are based on one unique individual so lack
generalisability. However the information gathered from case studies has been confirmed by other studies
therefore although the results may be unique they also offer a good insight into the theory.
4. Early studies: included the use of artificial light which may have affected their cycle.

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Ultradian rhythms
Those which occur more than once in a 24 hour period, for example the sleep cycle which repeats approximately
four times per night. The stages of sleep repeat roughly every 90 minutes while asleep.
Another example of an ultradian rhythm is the basic rest-activity cycle: this cycle shows that sleep stages are part
of a continuum. This theory coined by Kleitman assumes that the 90 minute cycle between SWS and REM that
occurs during sleep continues over the 24 hours of the day.…read more

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Infradian rhythms
Those which occur over a period greater than 24 hours, such as the menstrual cycle and seasonal affective
Seasonal affective disorder is where low light levels stimulate melatonin production and decrease serotonin
production. Terman et al. (1998) researched 124 participants with SAD; 85 were exposed to a bright light in the
morning or evening while others were exposed to negative ions and acted as a placebo group.…read more

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Endogenous pacemakers
Internal factors which are able to regulate biological rhythms.
To study these, Siffre (1962) spent 61 days in a cave in low light conditions. During this period, his body clock
extended to a 24.5 hour day and when he emerged he believed it was 28 days earlier than it in fact was.…read more

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Exogenous Zeitgebers
External time cues to help regulate biological rhythms and synchronise them. Endogenous pacemakers and
exogenous zeitgebers need to work together in order to co-ordinate the behaviours they regulate with the external
environment (entrainment).
Light entrains the free-running biological rhythm. This affects the SCN and other peripheral oscillators. Campbell and
Murphy shone light on the back of participant's knees and reset circadian rhythms. Therefore blood may be a
messenger in the form of carrying light signals to the brain.…read more

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Disruption of rhythms
Jet lag is caused by the body's internal clock being out of sync with external cues and has symptoms including
fatigue, insomnia, anxiety and dehydration.
Schwartz et al. (1995) studied the performance and reaction times of baseball teams flying from the East to West
coast of America and vice versa (a 3 hour time difference). It was found that teams travelling West performed
considerably better than those travelling East.…read more

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This study had tangible real life benefits and applications.
Boivin et al. (1996) put 31 male participants on an inverted sleep pattern for three days. After waking on each day
they were subjected to one of the following conditions: very bright light, bright light, ordinary room lighting or dim
lighting. To measure the adjustment, core body temperature (a known circadian rhythm) was measured. Participants
in the very bright light condition adjusted by five hours within three days.…read more

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Evolutionary Theory of Sleep
The evolutionary theory proposed by Meddis states that due to poor vision in low light, sleep has an evolutionary
advantage to humans because it keeps the species safe at night; and therefore more likely to survive to pass on
genes. This theory also takes into account that animals with higher metabolic rates spend more time eating and so
sleep for smaller periods at a time.…read more

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