Biological Rhythms and Sleep

Brief summary of theories and studies including evaluation points  :)

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Circadian Rhythms

Sleep-wake cycle

run by endogenous pacemakers but needs correction from exogenous zeitgebers

-> Micheal Siffre aka 'cave man', spent 6 months in Texan cave away from external cues, found his circadian rhythm settled down to just over 24 hrs but sometimes 48

-> Aschoff & Wever, placed pp's in under ground WWII bunker away from cues, found people displayed rythms between 24-25 hrs but some 29 hrs

shows external cues important in regulating biological rythms = entrainment


- early research flaw -> not isolated from artificial light - Czeisler et al, altered pp's cricadian rhythms down to 22 hrs and up to 28 hrs using dim lighting

- cycle length -> research has found cycles can vary between 13 to 64 hrs (Czeisler et al)

- cylce onset -> different innate patterns of sleeping and waking, Duffy et al, found there are morning types and evening types.

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Circadian Rhythms

Body temperature

lowest at 4:30am approx 36 celcius, highest at 6:30pm approx 38 celcius

post lunch dip -> not related to food intake

Wright et al, propsed higher body temperature leads to increased physiological arousal leading to improved cognitive performance

Hord & Thompson, tested this idea in a field experiment and found no correlation

Follard et al, learning abilty of 3 year olds, read stories at either 9am or 3pm, week later the 3pm at superior recall and retatined 8% more meaningful information, also had a higher body temperature


- cause or correlation -> not clear whether increased cognitive performance is due to higher body temperarture or high temperature leads to increased arousal.

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Ultradian Cycles

Basic Rest Activity Cylce -> BRAC

90 minute cycle of rest followed by activity

Friedman & Fisher, observed psychiatric patients over a 6 hour period and found a clear 90 minute cycle of eating and drinking behaviour

BRAC ensures that biological processes in the body work in unison by acting as a conductor, ensuring the body has what it needs to function so bodily rhythms can run properly

Stages of sleep.......BAT-D

awake brain = Beta wave

stages 1 & 2 -> relaxed alpha waves, as heart rate slows changes to theta waves

stages 3 & 4 -> deep sleep of SWS signalled by delta waves, metabolic rate slows and growth hormone is produced

REM sleep -> know as 'paradoxical sleep', associated with dreaming

Dement & Kleitman, demonstrated people woken up in REM were usually dreaming, but not exclusive people found to be dreaming in NREM

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Infradian Rhythms

Menstrual Cycle

determined by fluctuating level of hormones

Pituitary gland releases FSH & LH, egg ripens and triggers the release of oestrogen and later proestrogen used to maintain the uterus lining

no pregnancy after 2 weeks, progesterone levels fall and lining is shed

mens monthly cycle:

Empson, experiment into male patterns using body temperature and alertness, found some evidence for periodic variation


can be controlled exogenously -> Russell et al, showed pheromones can entrain the menstrual cycle by collecting sweat from one group and wiping it on the upper lip of another group, menstrual cycles synchronised

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Infradian Rhythms

seasonal effective disorder (SAD)

yearly cycle of depression starting in the winter and then recover in the summer

sufferers have low moods during the winter -> darker causes imbalance in hormones

melatonin secreted at night -> darker = more secreted

melatonin inhibits serotonin -> leading to symptoms of depression


- alternative explanation -> could be caused by a disrupted circadian rhythm (hormones follow a 24 hour cycle), we go to bed earlier because its darker putting the rhythms out of sync

+ real world application -> photo-therapy developed to treat SAD

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Endogenous Pacemakers

Suprachiasmatic nucleus (SCN)

tiny cluster of nerves found in the hypothalamus just above the optic chiasm

receives information about light, which enters via the optic nerve in the eye (also happens when eyes are shut)

light confuses SCN as it rises at different times -> exogenous zeitgebers entrain the SCN

SCN is a pair of structures: ventreal = quickly reset by external cues & Dorsal = less affected by light, harder to reset


+ role of SCN -> Morgan, bred mutant hamsters that altered circadian rhythm, when SCN was transplanted into normal hamsters they exhibited mutant rhythm -> - issue of using animals for scientific research

+ can explain effects of desynchronisation -> occurs when ventreal & dorsal sections are out of phase, 

-> evidence from Kate Aldcroft, lived in cave for 25 days, body temperature and sleep patterns out of sync, had symptoms similar to jet lag

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Exogenous Zeitgebers

external time givers e.g. light, temperature and social cues

light -> affects SCN, Campbell & Murphy, altered pp's circadian rhythms by shining light on the back of their knees

temperature -> triggers hibernation and deciduous trees to lose the leaves

social cues -> eating triggers liver and kidney cells to reset


- early studies exposed to artificial light -> assumed it wouldn't affect rhythms but Campbell & Murphy proved otherwise

-> Boivin et al, claimed that artificial light is effective but brighter lighting is better

in reality endogenous and exogenous cues work together as one system -> in the real world you are never totally isolated 

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Disruption of Biological Rhythms

shift work

decreased alertness -> cortisol levels lower at night and body temperature is lower

sleep deprivation -> sleep during day disrupted by noise and daylight

health -> causes rhythms to go out of sync, more susceptible to illnesses


+ real world application -> country relies on shift work, essential we know the effects and how to reduce them

alternative explanation -> effects not just caused by disruption of rhythms but also social deprivation and family disruption

+ research found ways to reduce negative effects -> Bambra, forward rotating shifts are less damaging as they follow logical order of the day

+ real world application -> artificial light can be used to entrain rhythms and reduce negative impacts

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Disruption of Biological Rhythms

Jet lag

physiological effects of disrupted rhythms, symptoms include insomnia, nausea and depression

Dorsal proportion of SCN takes longer to adjust to large changes

Phase delay = easier to adjust (same as staying awake later) travelling east to west

Phase advance = harder to adjust, travelling west to east


- alternative explanation -> jet lag due to other factors to do with travelling e.g. annoyance and long hours

+ melatonin can be used to reduce effects -> Herxeimer & Petrie, meta analysis of 10 studies found its effective when taken just before sleep

+ social cues -> eat and sleep at right times, Fuller et al, period of fasting followed by eating at the right time effective in entraining rhythms

+ phase advance -> Recht et al, analysed baseball results over 3 years, found when travelling east to west teams won more (44% compared to 37%)

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Lifespan Changes


babies sleep 16hrs +, not continuous have a clear 90 minute cycle, by 6 months they have a clear sleep wake cycle with a few naps

immature version of REM and SWS called active and quiet sleep


evolutionary -> sleep patterns evolved so parents can get on with daytime activities e.g. foraging and hunting

biological -> active sleep associated with production of neurotransmitters and consolidation of memory


sleep around 12hrs and gradually decreases, same EEG pattern as adults

parasomnias -> sleep walking and night terrors common


cultural differences -> Tynjala, sleep patterns across Europe vary e.g Israel sleep 9hrs and Swiss 10hrs -> suggests cultural values and lifestyles influence sleep

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Lifespan Changes

Old age

difficulty going to and staying asleep -> wake frequently only have 5% SWS and 20% REM

phase advance -> got to bed earlier and wake earlier, nap during day to satisfy sleep needs


reduced sleep due to physiological changes -> less SWS means they are easily woken

explains symptoms of old age -> less growth hormone produced

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Lifespan Changes


duration increase, boys experience *********** during sleep, phase delay -> stay awake later and wake later


explained by hormone changes -> major changes in sex hormone, mainly produced at night so disrupts sleep -> explains symptoms associated with teenagers e.g. moodiness

real world application -> Wolfson & Carskadon, school should fit around delayed sleep syndrome (typical of teenagers) which means they have poor attention spans in the morning


typically 8hrs a night -> 25% REM, increased frequency of sleep disorders


too much sleep not good -> Kripke, 6-7 hrs associated with reduced mortality but more than 10 hrs can increase mortality by 30%

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Functions of Sleep

Restoration theory

Horne, function of sleep is to rest and recuperate in order to restore body to its ful working capactiy

Oswald, period of time which body an recuperate, SWS initiates body repair and REM brain repair

- Growth hormone (GH) produced -> used in protein synthesis

- implies while awake we deplete in chemicals, therfore sleep is like cathcing your breath after exercise

- REM initiates brain repair -> neurotransmitters not produced so gives them a chance to restore sensitivity


+ plauable explanation -> know the effects of sleep deprivation

+ premature babies -> 90% of sleep time is REM so brain can grow and develop

+ GH -> Vancaulter & Plat, amount of GH produced correlated with amount of SWS

- amino acids used in protein synthesis only stay in the body for 2 hours -> don't eat at night so protein synthesis can't occur

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Functions of Sleep

Evolutionary theory

Kleitman, sleep forces us to conserve energy at times when it would be inefficient to be awake -> especially true of warm blooded animals that use energy to maintain temperature

Meddis, sleep keeps animals inconspicuous and safe from predators at times when they couldn't effectively feed

foraging requirements -> amount of sleep depends on food requirements

habitat safety -> sleep constrained by risk of predation


+ energy conservation -> Berger & Philips, mammals body temperature falls about 1 degree when asleep

+ species sleep time varies

- energy conservation only present in NREM -> why has REM evolved if it has no function

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Sleep Disorders


problem with falling or staying asleep

primary = no apparent medical or physiological cause

secondary = consequence of something else e.g. medical problem

Risk factors

age -> common in teenagers due to phase advance, older people have increasing physiological problems

gender -> increased incidence in women due to hormonal changes

personality -> insomniacs tend to internalise psychological disturbances


+ distinction between the type of insomnia is important in deciding appropriate treatments -> treat either the insomnia or the underlying cause

+ age -> Roberts et al, survey of 4000 11-17 year olds, 25% experienced insomnia, 5% reported impaired ability to function and 41% reported continuing problems

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Sleep Disorders

Sleep walking

common in children -> affects about 20% but only 3% of adults

due to incomplete arousal -> brain not awake fully

display EEG patterns with a mixture of delta and beta waves


+ explained by lifespan changes -> children have more SWS so its more likely to occur

+ real world application -> Jules Lowe killed his 80 year old father but found not guilty of murder because he was sleep walking

+ Oliviers, system that inhibits motor activity in SWS not fully developed in children

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Sleep Disorders


uncontrollable attacks of sleepiness at irregular and unexpected times, can last minutes or seconds

symptoms include fatigue and cataplexy


malfunction of REM sleep -> popular during 1950s, plausible symptoms that match REM sleep e.g. paralysis

Mutation in HLA -> HLA part of immune response, mutation found in narcoleptics (Honda et al)

mutation in hypocretin -> hypocretin maintains wakefulness, Linn et al found a mutation of gene that produces hypocretin in narcoleptic dogs


biological vs. psychological approach -> most explanations biological but Lehmann & Weiss suggest it disguises sexual fantasies

mutation of REM sleep -> Vogel, found that REM patterns are present just before an episode

HLA not sole explanation -> Mignot et al, found HLA mutation found in  in general population

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