Biological Rhythms & Sleep

A2 psychology revision

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  • Created on: 16-06-11 15:13

Biological Rhythms

Circadian: occur every 24hrs - e.g. sleep-wake cycle

Infradian: occur less than once a day - e.g. mestruation & seasonal affective disorder (SAD)

Ultradian: occur more than once every 24hrs - e.g. stages in sleep & breathing

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Role of Endogenous Pacemakers

Circadian Rhythms

SCN in hypothalamus = 'internal clock' - it is sensitive to light & regulates the pineal gland - amount of melatonin produced alters according to light conditions

Menaker et al: leisoned this structure in hamsters = sleep-wake cycle disrupted

DeCoursey: destroyed SCN in chipmunks - became more active at night

Pengelly & Fisher: squirrels will hibernate even in lab - completely determined by endogenous factors (BUT humans can adapt more easily by changing environment)

Infradian Rhythms

McClintock: collected samples of pheremones & found 68% of pps responded to having them wiped under their nose - mestruation cycle shortened/lengthened depending on sample

Rusell et al: 4 out of 5 pps had menstrual cycles that synchronised to within a day of 'pheremone donor' after 5 months

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Role of Exogenous Zeitgebers

Circadian Rhythms

Siffre: cave study - allowed to 'free run' - sleep-wake cycle extended to 25-30hrs without clocks or natural light

Miles et al: case study of a blind man - had to take stimulants/sedatives to regulate 24hr cycle

Infradian Rhythms

Binkley: blocking out mooon light & using artificial light affects menstrual cycle

Terman et al: SAD - 60% of pps showed improvements to light therapy when given in morning


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Disruption to Biological Rhythms

Consequences of Shift Work

Boivin et al: decreased alertness - night workers experience a 'circadian trough' during shift

Tilley & Wilkinson: sleep deprivation - daylight sleep in shift workers is typically 1-2hrs shorter with REM in particular affected

Knuttson et al: effects on health - shiftworkers for over 15yrs are 3x more likely to develop heart disease

Soloman: social disruption - divorce rates in shiftworkers may be as high as 60%

Reducing Harmful Effects

Czeisler et al: recommended 21 day shifts & moving shifts forward (phase delay) for factory workers - productivity & satisfaction increased after 9 months

Bambra et al: following the logical pattern of the day may be easier & less damaging (supports Czeisler)

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Disruption to Biological Rhythms

Affecting Factors in Jet Lag

Wegman et al: direction of travel - travelling East to West easier to adapt to (phase delay)

Sack et al: age - jet lag decreases with age

Individual differences: 'phase tolerance'

Cumulative factors: bad nights sleep before flight, drinking alcohol or caffeine, noise, annoying passengers etc.

Effects of Jet Lag (performance decrement)

Schwartz et al: baseball teams from east coast of USA got better results travelling west than west coast teams to east

Recht et al: US baseball results showed teams who travelled E-W won 44% on average whereas those who travelled W-E won 37%

Reducing Effects

Fuller et al: social customs - a period of fasting followed by eating on new time scale should help entrain bio rhyhtms

Petrie: melatonin - can be very effective when taken near bedtime

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Nature of Sleep

Sleep cycle

5 phases of sleep

Most people experience 5 complete cycles, each lasting 90-110 mins

Stage 1: light sleep, eye & muscle activity slow, sudden muscle contractions & hypnogogic hallucinations

Stage 2: eye movement & muscle activity stops, brain waves slow (THETA waves), short bursts of high freq. sleep spindles, K-complexes

Stage 3: still no eye/muscle movement, DELTA waves, leads into deep sleep

Stage 4: SWS - long, slow DELTA waves, body temp. heart rate & blood pressure at lowest point, growth hormones secreted, sleepwalking & night terrors can occur

REM: heart rate & breathing increases, eye movement quick & irregular, blood pressure rises, muscles paralysed from neck down, brain very active (BETA waves), most dreaming occurs

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Lifespan Changes in Sleep

New born babies: tend to sleep for aorund 2 thirds of the day (16hrs), display 2 kinds of sleep - quiet & active ('immature' versions of SWS & REM)

More active sleep at birth & even more for premature babies - can be explained in terms of brain development

Also suggested to be an adaptive mechanism to make parents' lives easier

Childhood: (1 year) gradual maturation of sleep patterns, consolidation of sleep periods, (5 years) full EEG patterns with different frequencies to adults, most sleep for around 10hrs, instances of parasomnias

Adolescence: sleep on av. 9-10hrs a night, less REM than childhood, circadian rhythms change - delayed sleep phase - may be linked to hormonal changes (Crowley et al)

Middle age: shallowing & shortening of sleep, loss of hormones (menopause) in late middle age = want to go to bed earlier & suffer from sleep deprivation

Old age: REM decreases to about 10%, stage 2 increases to 60% of sleep time, amount of SWS reduces, have more difficulty getting to sleep & wake up more frequently = phase advance of circadian rhythms, reduced sleep partly a consequence of physiological changes

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Differences in Nature of Sleep

Cultural Differences

Tynjala et al: Israeli children slept 8.5hrs on average, whilst Swiss slept 9.5hrs

Shin et al: Korean children slept 6.5hrs on average, whilst Iranian slept 7.7hrs

Most evidence comes from EEG's = controlled & objective BUT creates unfamiliar sleeping environment

However... Empson: after 1st night, pps adjust to conditions

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Function of Sleep

1, Restoration Theories

Oswald: all stages of sleep important - REM for brain & NREM for body (growth hormones secreted in SWS)

+ Supported by total sleep deprivation studies (e.g. Rechtschaffen & Peter Tripp/Randy Gardner case studies)

Horne: sleep only provides repair for brain (REM only important stage) - 'core sleep' & 'optional sleep' (NREM)

+ Supported by partial sleep deprivation studies (e.g. Jouvet)

2. Evolutionary Theories

Meddis: 'waste of time' hypothesis - sleep helps animals stay out of the way of predators when most vulnerable

Webb: hibernation theory - sleep is a period of enforced inactivity to conserve energy



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Disorders of Sleep - Insomnia

Primary Insomnia

Insomnia is primary problem - no known cause

May have developed bad sleeping habits but could also be due to expectations of sleep difficulty or use of stimulants

Secondary Insomnia

Insomnia is a symptom of underlying medical, psychiatric, or environmental cause

Typical of those who do shift work/have circadian rhythm disorders but could also be due a result of caffeine or alcohol

Risk factors

Age, gender, anxiety/expectation of sleep difficulty, sleep apnoea - factors which make throat narrow during sleep cause sleeper to wake, personality - Morin et al: insomniacs rated impact of minor events & intensity of major events higher

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Disorders of Sleep - Insomnia

Treatments

Behavioural modifications: attribution therapy, sleep restriction, reconditioning, improving sleep hygiene

Phototherapy (artificial lighting)

Drugs: melatonin

Evaluation

Chronic insomnia unlikely to be explained by 1 factor - complicated disorder

Important to distinguish between primary & secondary insomnia - implications for treatment

Ohayon & Roth: casts doubt on idea of secondary insomnia - found it more often preceded than followed mood disorders

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Disorders of Sleep - Narcolepsy & Sleepwalking

Narcolepsy explanations

1. REM: malfunction in system regulating REM - supported by recordings of neuron activity in narcoleptic dogs - Siegel: cataplexy linked to activation of cell usually only active in REM

2. HLA: (human leukocyte antigen) - mutation of immune system, Honda et al: increased freq. in 1 type of HLA, 1 specific variation mostly found BUT not in all

3. Hypocretin: neurotransmitter (aka orexin) - appears to play important role in maintaining arousal/wakefulness, Lin et al: narcoleptic dogs w/ mutation in gene had disrupted processing of hypocretin, findings have been confirmed in human studies HOWEVER - Mignot: not found to be concurrent in twins (25-33%)

Sleepwalking

Hublin et al: 20% of children affected (3% of adults) - Oliviero: system that stops motor activity not yet developed

Incomplete Arousal: EEG's show a mixture of delta waves (SWS) & beta waves (awake state)

Genetics: 50% concordance in MZ twins - Broughton: 10x greater prevalence in 1st degree relatives

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