Psychology Sleep Chapter Summary

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Circadian Rhythms Summary

Sleep-wake cycle:

  • Circadian = 24 hours
  • Cycle persists despite isolation from light

Evaluation:

  • Participants not isolated from artificial light in early research
  • Demonstrated by Siffre and Aschoff and Weaver
  • External cues important too (Folkard et al)
  • Cycle length varies in individuals
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Circadian Rhythms Summary

Core Body Temperature:

  • Lowest at 4:30am
  • Highest at 6pm
  • Post-lunch dip, even without food

Evaluation:

  • Linked to cognitive abilities (Folkard et al)
  • Evidence that change is caused by temperature (Giesbrecht et al, 1993)
  • Other research sugest link is spurious
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Circadian Rhythms Summary

Hormones:

  • Cortisol = lowest at midnight
  • Melatonin and growth hormone = highest at midnight
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Circadian Rhythms Summary

IDA:

  • Biological and deterministic
  • Real world application - chronotherapeutics
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Infradian and Ultradian Rhythms Summary

Ultradian Rhythms:

  • Less than one day
  • First four stages of sleep = NREM
  • Fifth stage = REM
  • BRAC = 90 minutes within 24 hour rhythm

Evaluation:

  • REM does not equal dreaming
  • BRAC = important because it ensures biological processes work in unison
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Infradian and Ultradian Rhythms Summary

Infradian Rhythms:

  • Female menstrual cycle regulates ovulation
  • Males have 20 day cycle of body temperature and alertness
  • SAD = caused by melatonin during winter months

Evaluation:

  • Menstrual cycle = subject to exogenous cues
  • PMS
  • SAD could also be consequence of disrupted circadian rhythms
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Infradian and Ultradian Rhythms Summary

IDA:

  • Determisitic but can change through willpower (Born et al)
  • Real world application = phototherapy
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Endogenous Pacemakers and Exogenous Zeitgebers

Endogenous Pacemakers:

  • SCN = main endogenous pacemaker
  • Contains protein mechanism
  • Pinal gland controls melatonin secretion

Evaluation:

  • SCN evidence = 'mutant' hamsters (Morgan)
  • Desynchronisation can lead to symptoms of jet lag
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Endogenous Pacemakers and Exogenous Zeitgebers

Exogenous Zeitgebers:

  • Light is dominant zeitgeber
  • Social cues also important
  • Biological rhythms can be entrained by temperature

Evaluation:

  • Artificial lighting may also reset biological clock
  • Failure of biological clock leads to sleep-phase disorders
  • Biological clck is really a blend of endognous and exogenous factors
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Endogenous Pacemakers and Exogenous Zeitgebers

IDA:

  • Non-human animal studies
  • Ethics and relevance
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Lifespan Changes

Children:

  • Babies sleep 16 hours a day, but not continuously
  • Shorter sleep cycles than adults
  • Circadian rhythm established at six months
  • At 5, sleep patterns like those of adults
  • May experience parasomnias

Evaluation:

  • Sleep differences in babies - adaptive (for parents)
  • Immature brain
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Lifespan Changes

Adolescence:

  • Need for sleep increases (9-10)
  • Circadian rhythms change
  • Slight phase delay

Evaluation:

  • May be linked to hormone production
  • Implications in school day
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Lifespan Changes

Adulthood and Old Age:

  • Increase in sleep disorders
  • Patterns of sleep changes in old age
  • Reduction in REM and SWS
  • Older = phase advance effect

Evaluation:

  • Increased mortality rate with too much sleep (Kripke et al)
  • Sleep deficit in old age may explain impaired functioning in other areas
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Lifespan Changes

IDA:

  • Developmental Approach
  • Cultural bias (overlooked)
  • Real-world application
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Restoration Explanations

SWS:

  • SWS = stages three and four
  • Growth hormones secreted during SWS
  • Decline of GH in older age = reduced SWS
  • Lack of SWS = low immune functioning

REM:

  • Important for brain growth
  • Restoring neurotransmitter sensitivity
  • Link between REM and procedural memory
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Disruption of Biological Rhythms

Shift work and Shift Lag:

  • Nightworkers experience 'trough' of decreased alertness
  • Sleep deprivation due to sleeping problems during the day
  • Relationship between shift work and organ disease

Evaluation:

  • Shift work effects not solely due to disruption of biological rhythms
  • More problems with rotating shifts
  • Forward rotating less harmful
  • Artificial lighting can eset rhythm but not dim lighting
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Disruption of Biological Rhythms

Jet travel and Jet lag:

  • Caused by disruption of circadian rhythms
  • Phase delay less disruptive than phase advance

Evaluation:

  • Jet lag symptoms may be caused by other factors
  • Melatonin may reduce symptoms
  • Social customs also help
  • Individual differences exist in coping with disruption
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Evolutionary Explanations:

Energy Conservation:

  • Period of inactivity to conserve energy
  • Essential for animals with high metabolic rates

Foraging:

  • Herbivores spend less time sleeping
  • Carnivores more because food rich in nutrients

Predator Avoidance:

  • Sleep constrained by predation risk
  • Predators sleep more, prey sleep less

Waste of time:

  • Staying still at times when an animal cannot forage
  • Subject to predatation
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Evolutionary Explanations:

Evaluation:

  • Evidence about animal sleep patterns incomplete
  • Evidence suggests that species with a higher metabolic rate sleep more
  • Evidence suggests that species with higher predatation risk sleep less
  • Evidence to support foraging and predator avoidance
  • NREM evolved first for energy conservation
  • Then REM to maintain brain activity
  • Phylogenetic signal supports evolution of sleep patterns
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Evolutionary Explanations:

IDA:

  • Evolutionary approach can be combined
  • Restoration using core and optional sleep
  • Horne (1988)
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Explanations of Insomnia

Short term Insomnia:

  • Caused by worry, noise, jet lag or temporary medical conditions

Long term Insomnia:

  • Primary = not associated with medical conditions
  • Secondary = symptom of a medical disorder or some other issue
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Explanations of Insomnia

Evaluation:

  • Diagnosis has implications for treatment
  • May be cause rather than effect
  • Consequences include cognitive impairment, accidents, psychological disturbance, anxiety disorders or immune system underfunctioning
  • Predisposing factors (genetics)
  • Precipitating factors (environemental stressors)
  • Perpetuating factors (expectations)
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Explanations of Narcolepsy

  • Psychological (Disguishing sexual fantasies)
  • Early explanations = failure of REM regulation
  • HLA mutation causes reduced immune system functioning
  • Low levels of neurotransmitter hypocretin in hypothalamus affects wakefulness 

Evaluation:

  • REM hypothesis (some evidence, not convincing)
  • HLA varient cannot be sole explanation because common in general population
  • Hypocretin support from studies of dogs and humans
  • Low levels of hypocretin rarely inherited
  • Most likely to due brain injury or autoimmune attack
  • Link to HLA
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Explanations of Sleep Walking

  • Person wakes during SWS but brain arousal incomplete
  • Other factors = sleep deprivation, alcohol, hormone changes
  • May affect children more because underdeveloped SWS inhibition

Evaluation:

  • Evidence for genetic basis
  • Diathesis-stress model
  • Sleep deprivation triggers sleep walking in vulnerable people
  • Psychological cause unlikely because not in REM sleep
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