Sleep Key Studies Summary

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The Circadian Rhythm

Siffre (1975)

  • 61 days in the Southern Alps = resurfaced believing the date was 20th august
  • Six months in a Texas Cave 
  • Natural rhythm settled to just over 24 hours, this would sometimes change dramatically to as much as 48 hours, however.
  • Final experiment = 60 years old 
  • Internal clock ticked more slowly than when he was a young man 
  • His sleep patterns also changed 

Czeisler et al (1999) 

  • Altered participants' circadian rhythms down to 22 hours and up to 28 hours
  • Just using dim lighting
  • Different people can vary from 13 to 65 hours 

Duffy et al (2000)

  • Found that morning people prefer to rise early and go to bed early 
  • Evening people prefer to wake and go to bed later 
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Infradian Rhythms

Dement and Kleitman (1957)

  • Woke participants at the times when their brain waves were characteristic of REM 
  • Participants were highly likely to report dreaming 
  • Dreams were also recorded outside REM slee 
  • Not always dreaming during REM sleep
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Ultradian Rhythms

Russell et al (1980)

  • Daily samples of sweat were collected from one group of women
  • Rubbed on the upper lip of women in a second group
  • Groups = kept seperate
  • Menstrual cycles became synchronised with their individuals odour donor 
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Endogenous Pacemakers

Morgan (1995)

  • Bred 'mutant' hamsters 
  • Circaidan rhythms of 20 hours instead of 24 hours
  • Transplanted their SCNs into normal hamsters
  • Normal hamsters displayed the mutant rhythms

Folkard (1996)

  • Spent time in a cave
  • 25 days = temperature rhythm was a 24 hour one 
  • Sleep rhythm = 30 hour cycle 
  • Led to symptoms similar to jet lag 
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Exogenous Zeitgebers

Boivin et al (1996)

  • Circadian rhythms can be entrained by ordinary dim lighting 
  • Bright lighting was mor eeffective

Stevens (2006)

  • Exposure to artificial light disrupts circadian rhythms 
  • Thus disrupts melatonin production 
  • Explain why women in industrialised societies are more likely to develop breast cancer 
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Shift Work and Shift Lag

Solomon  (1993)

  • Shift work effects might also be due to lack of sleep associated with having to go to bed at unusual times
  • Shift workers also experience social disruption as well as disruption to biological rhythms
  • Difficult to meet new friends and spend time with family
  • Divorce rates = 60% among all night shift workers

Gold et al (1992)

  • More problems with rotating shifts 
  • Non-fluctauating shifts are less disruptive 
  • Individual can get used to one sleep-wake pattern 

Bambra et al (2008)

  • Forward-rotating shifts may be less damaging
  • Rotating workers through shift changes more quickly is better fo health and work-life balance 
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Jet Travel and Jet Lag

Fuller et al (2008)

  • Period of fasting followed by eating on the new time schedule
  • Help entrain biological rhythms 
  • Body clocks are reset by food intake 

Herxheimer and Petrie (2001)

  • Reviewed 10 studies 
  • Found that where melatonin was take near to bed-time, it was effective
  • If taken at the wrong time = delay adaptation

Gronfier et al (2007)

  • Able to enrain circadian rhythms to longer thn 24 hours just by using bright light pulses 
  • Modulated by light exposure 
  • Artificial lighting is moderately effective in re-setting the rhythm
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The Nature of Sleep and Lifespan Changes

Crowley et al (2007)

  • Hormonal changes can explain the upset to the circadian clock
  • Delayed sleep phase syndrome

Wolfson and Carskadon (2005)

  • Schools should begin later to accommodate the poor attention spans of adolescents in the early morning 

Kripke et al (2002)

  • Surveyed over 1 million adult men and women 
  • 6 hours sleep = reduce mortality risk 
  • 8 hours = 15% increase risk of death 
  • 10 hours = 30% increase risk of death 
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Restoration Theory

Williams et al (1959)

  • Participants deprived of sleep for more than 72 hours 
  • Invariably had short period of microsleep while apparently awake
  • EEG recordings shows that microsleep is the same as sleep

Rechtschaffen et al (2005)

  • Forced rats to remain physically active by rotating a disc that they were standing on each time they started to fall asleep
  • 33 days = all sleep-deprived rats died 
  • Stress could have been the cause of death, and not sleep deprivation 

Rattenborg et al (2005)

  • Conducted a similar experiment with pigeons 
  • Suffered no ill effects
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Evolutionary Explanation

Zepelin and Rechtschaffen (1974)

  • Small animals sleep more than larger animals
  • Supports the view that energy conservation might be the main reason for sleep 
  • Exceptions = sloths (20 hours a day)

Alison and Cicchetti (1976)

  • Species who had a higher risk of predation did sleep less 
  • Exceptions = rabbits that sleep as much as moles 
  • Larger animals had less NREM sleep but not less REM sleep
  • NEM = important to energy conservation 

Horne (1988)

  • Theory that combines elements from both restorative and adaptive theories
  • Distinction between core and optional sleep
  • Core = SWS sleep 
  • Options = dispensable and occupies unproductive hours 
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Insomnia

Ohayon and Roth (2003)

  • 15,000 Europeans 
  • Insomnia more often preceded than followed cases of mood disorder 
  • May be helpful to treatment insomnia regardless of primary/secondary effect 

Watson et al (2006)

  • Twin studies
  • 50% of the variance in the risk for insomnia could be attributed to genetic factors
  • Physiological factors may predispose a person to develop insomnia 

Epsie (2002)

  • Perpetuating factors are the key to chronic insomnia
  • For example = stress
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Insomnia

Ohayon and Roth (2003)

  • 15,000 Europeans 
  • Insomnia more often preceded than followed cases of mood disorder 
  • May be helpful to treatment insomnia regardless of primary/secondary effect 

Watson et al (2006)

  • Twin studies
  • 50% of the variance in the risk for insomnia could be attributed to genetic factors
  • Physiological factors may predispose a person to develop insomnia 

Epsie (2002)

  • Perpetuating factors are the key to chronic insomnia
  • For example = stress
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Insomnia

Ohayon and Roth (2003)

  • 15,000 Europeans 
  • Insomnia more often preceded than followed cases of mood disorder 
  • May be helpful to treatment insomnia regardless of primary/secondary effect 

Watson et al (2006)

  • Twin studies
  • 50% of the variance in the risk for insomnia could be attributed to genetic factors
  • Physiological factors may predispose a person to develop insomnia 

Epsie (2002)

  • Perpetuating factors are the key to chronic insomnia
  • For example = stress
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Narcolepsy

Lehrman and Weiss (1943)

  • Sudden sleepiness disguises sexual fantasies

Vogel (1960)

  • The REM Hypothesis
  • Observed REM sleep at the onset of sleep in a narcoleptic patient
  • Supported by findings of neuron activity in the brainstem of narcoleptic dogs 
  • Showed that cataplexy is linked to the activation of cells that in normal animals are only active during REM sleep  

Mignot et al (1997)

  • Narcolepsy-HLA Link
  • Most commonly found in narcoleptics but also in general population
  • Cannot be sole explanation 

Mignot (1998)

  • Low levels of hypocretin are unlikel to be due to inherited factors
  • Human narcolepsy doesn't run in families
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Sleep Walking

Lecendreux et al (2003)

  • 50% concordance in identical twins 
  • 10-15% in non-identical twins 
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