Biological Rhythms and Sleep Studies

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Siffre 1975

  • Spent 6 months in a cave with no exogenous zeitgebers so his biological clock was free running.
  • It was found that his sleep wake cycle extended to 25-30 hours and his body temperature became more stable.
  • This shows that in the absence of light cues, endogenous pacemakers have a strong influence upon circadian rhythms; however this regulation is not perfect suggesting that exogenous zeitgebers are important too. 
  • There must be two separate endogenous pacemakers for the sleep wake cycle and body temperature because they become desynchronised.
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Siffre 1975 Evaluation

  • Case study therefore not generalisable
  • Support for Siffre came from Wever (1979) found Ps had a 25-27 hr. sleep wake cycle in the absence of light cues. Key variables were controlled.
  • This was the first time that this occurred so they could not predict the effects – no protection from harm.
  • He also reported long-lasting psychological consequences and was not offered any type of counselling. 
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Morgan 1995

  • When Morgan removed the SCN from hamsters, their circadian rhythms disappeared. 
  • Once they were transplanted back in from foetal hamsters they reappeared. 
  • Also bred mutant hamsters with 20 hour circadian rhythms and transplanted their SCN into normal hamsters and they took on the 20 hour circadian rhythm.

Evaluation: Animal studies may not be generalisable to humans.

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Miles 1977

  • Studied a man blind from birth who had a strong circadian rhythm of 24.9 hours.
  • Despite being exposed to other exogenous zeitgebers (clocks & radios) he could not reduce his sleep wake cycle to 24 hrs.
  • This shows that light was needed to adjust his sleep wake cycle to day length.

Evaluation: Case study = not generalisable

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Luce and Segal 1966

  • In the Arctic Circle people can still sleep at night during the summer even though the sun never sets.
  • Other cues become dominant, e.g. social cues such as meal times dictate when it is time to get up or get up.
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Folkard et al 1977

Tested LTM recall in 12/13 yr olds and learned that recall was better at 3pm when their body temperature was higher rather than at 9 am when body temperature was lower. 

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Schochat et al (1997

Role of melatonin – 6 male Ps in a sleep lab and measured their tendency to sleep at different times of the day and the amount of melatonin in their blood 3 times per hr. A correlation was found between increased melatonin levels and increased tendency to sleep.


+ supported by medical research as melatonin is used to treat insomnia.

- Unnatural sleep conditions in the lab which may not reflect natural sleep-wake cycles. 

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Hawkins and Armstrong-Esther 1978

  • Studied 11 nurses working night shifts.
  • Found their performance was initially poor supporting the link with poor concentration but improved over the week as their circadian rhythms gradually adjusted. 
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Czeisler et al (1982)

  • Studied shift workers in a chemical plant in Utah, who had shifts rotating backwards (phase advance).
  • They found the workers to have high illness rates, sleep disorders and high levels of stress, suggesting that their internal body clocks were out of synchronisation with external zeitgebers.

 Applications of Research -  They persuaded managers to use a phase delay for shifts and change them every 21 days instead of 7, giving time for adjustment. 9 months later it was found that workers were healthier and more content and there was increased productivity and fewer errors.

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Klein et al (1972)

  • Flew 8 Ps between USA and Germany.
  • Found adjustment was easier when flying East to West regardless whether the flight was inward or outbound. 
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Webb and Agnew (1971)

  • Found that successful strategies for coping with jet lag include: outdoor pursuits, exposure to light and regular mealtimes.
  • It is advised to follow the exogenous zeitgebers of the destination.
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Russell et al. (1980)

  • Collected underarm sweat of donor women and placed it on the upper lip of femal Ps.
  • Repeated daily for 5 months.
  • A control group had the same treatment but with no sweat/pheromones.
  • The Ps did not know what group they were in.
  • 4/5 of the Ps in the pheromone group synchronised their menstrual cycles with that of the donor.
  • Suggesting that pheromones act as an exogenous zeitgeber and can entrain the menstrual cycle.
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Rosenzweig et al 1999

  • Reported on Seasonal Affective Disorder (SAD)
  • This is a depression linked to the seasons, usually at the onset of Winter and increased hours of darkness. 
  • Darkness increases melatonion production and light reduces it. 
  • A sufferer experiences depression and becomes more lathargic and sleepy whilst often over-eating. In the summer the reverse happens and they become elated, more active and thinner. 
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Bentley 2000

  • Evolutionary advantage for womens menstrual cycles synchronising, allows women to have synchronised pregnancies and share childcare duties.
  • All women in the group can breastfeed at the same time, this is helpful if the mother died.
  • It is adaptive because it increases the chance of the baby surving to reproduce.
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Kleitman 1963

  • Amount of time spent in REM sleep decreases as we get older
  • Premature Babies = up to 80%
  • Newborn Babies = 50%
  • Children = 30%
  • Adults = 25%
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Kales and Kales 1974

  • Found that elderly people are more likely to wake up several times during the night in comparison to younger people.
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Van Cauter et al 2000

  • Examined several sleep studies involving male Ps
  • Sleep duration was found to decrease between two life periods:
  • 17 and 25, and between 35 and 50
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Floyd et al 2007

  • Reviewed 400 sleep studies and found that REM sleep decreased by about 0.6% per decade.
  • Its proportion increases from age 70, though this may be due to sleep duration decreasing.
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Eaton-Evans and Dugdale 1988

  • Found that the number of sleep periods for a baby decreases until 6 months, then increases at 9 months then slowly decreases again. 
  • This may be due to teething problems.
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Tynjala et al 1993

  • Surveyed over 40,000 adolescents (11-16 yrs) from 11 European countries.
  • Israeli children slept the least on average - 8.5 hours 
  • Swiss children slept the most on average - 9.5 hours
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Oswald 1980

  • Believed that the high brain activity in REM sleep indicates that REM sleep is essential for brain growthand restoration, e.g. replace neurotransmitters, grow new synapses.
  • Also believed that growth hormone production during slow-wave sleep indicates that SWS is essential bodily growth and repair, e.g.  carry out protein synthesis, repair and replace cells.
  • 1969: Observed brain injured patients and found a significant increase in REM sleep. Suggested that this indicated brain recovery being undertaken.
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Horne 1988

  • Extended Oswalds original ideas
  • He proposed that core sleep (stage 4 of WS + REM) is essential for normal brain functioning in humans. In core sleep the brain restores itselfafter the days activities.
  • He claimed that the lighter stages of NREM sleep are not essential. Bodily restoration occurs during optional sleep and also during periods of relaxed wakefulness.
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Stern and Morgane 1974

  • Believed that during REM sleep neurotransmitters are replenished, supporting the idea of restoritive sleep.
  • Support for this comes from the action of anti-depressant drugs. These increase the levels of neurotransmitters s there is less REM activity. 
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Lavie et al 1984

  • Lack of REM sleep has no significant ill-effects
  • 33 yr old with shrapnel damage to head when aged 20. Reported almost no REM sleep since but lead a normal life- was a lawyer.
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Van Cauter et al 2000 & Van Cauter and Plat 1999

Van Cauter et al  2000

  • Found that the decrease in secretion of of growth hormone in older age has been associated with reduced SWS.

Van Cauter and Plat 1999

  • Found that the amount of growth hormone release is positively correlated with the amount of SWS, supporting a link between SWS and bodily restoration.

However, both are correlational studies and do not prove cause and effect. 

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Everson et al

  • Found that sleep deprivation in rats using the flowerpot technique caused:Suggests that REM sleep is essential for restoration, supporting restoration theory.
    • increased metabolic rate
    • loss of weight
    • lower resistance to desease 
    • death in about 19 days (immune system damage)
  • However rats are stressed to keep them awake and this may have caused the effects (ethical issues).
  • Also difficult to generalise to humans. 
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Dement 1960

Study of partial sleep deprivation

  • Volunteers in a sleep lab, woken as soon as they showed eye movement.
  • Deprivation of REM resulted in severe effects such as increased aggression and poor concertration.
  • Needed progressively more REM sleep to catch up, known as the REM rebound effect.
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Peter Tripp - Total sleep deprivation in humans

  • Stayed awake for 8 days, raising money for charity.
  • After 3 days he became abusive.
  • Then developed hallucinations and delusions.
  • By the end: his body temperature had dropped and his waking brain waves were like someone asleep.
  • However, he slept for 24 hours and fully recovered. 
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Meddis 1975

  • Predator Avoidance theory
  • Sleep evolved to keep animals safely hidden from predators at times of the day in which they are not required.
  • For most this means sleeping during darkness, hidden away from potential predators.
  • Therefore prey animals should sleep less as they are more at riskand need to be more alert to avoid predators, whereas predators can sleep for longer.
  • Meddis stated that this could also be called the 'waste of time' hypothesis. Sleep simply ensures that animals stay still when they have nothing better to do with their time.
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Allison and Cicchetti 1976

  • Studied the relationship between the sleep of 39 species animals in a lab and the degree of danger that species experienced in the wild. 
  • They found that the greater the environmental danger the less time an animal spent sleeping per day (negative correlation). 


  • There are exceptions e.g. rabbits were found to sleep as long as moles (8.4 hrs), rabbits had very high environmental danger whilst moles did not.
  • Data is correlational
  • Smaller animals have a higher metabolic rate that uses energy up faster. Small mammals sleep for much longer than larger animals. Sleep therefore serves a double purposeof conserving resources and keeping them safe from predators.
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Mukhametov 1987 - unilateral sleep

  • Dolphins must swim to the surface to take a breath. If they slept under water they would drown.
  • They have evolved a strategy where only one cerebral hemisphere of the dolphin's brain is asleep at a time, they other half stays awake. They swap over every 2-3 hours. 
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Webb 1982

  • Suggested that sleep is similar to hiberanation.
  • Provides a period of inactivity which conserves energy at times when it is harder to get food. 
  • Also described as hibernation theory. 
  • Warm blooded animals need to expend a lot of energy to maintain a constant body temperature.
  • Small mammals have a bigger problem as they have a high metabolic rate and use even more energy to keep warm or when foraging or escaping from predators so should sleep longer.
  • The percentage of the day spent asleep varies according to size and the amount of sleep is affected by other factors, foraging and predator avoidance. 

Foraging affects sleep patterns

  • Herbavores eat plants which are relatively poor in nutrients, they therefore spend alot of time eating and less time sleeping.
  • Carnivores eat food which is high in nutrients so do not need to eat continously. They can therefore 'afford' to spend time asleep so conserving energy. 
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Zepelin & Rechtschaffen 1976

  • Found a negative correlation between metabolic rate and total sleep time in a survey of 53 species of mammal indicating that smaller animals with a higher metabolic rate sleep for longer.
  • Found that smaller animals spend more hours asleep per day (bat- 20hrs) whilst larger animals sleep tend to sleep less (elephants - 4 hrs)
  • However, this is not true of all species as sloths are large and slow so should not need much sleep, yet Rattenborg et al 1976 found that they sleep for 20 hrs a day in captivity but only 6-9 in the wild.

Data is correlational does not prove a casual relationship.  

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Allison and Cicchetti 1976

  • During NREM sleep the brain uses less energy than REM sleep.
  • They found that larger animals had less NREM sleep not less REM sleep.
  • NREM sleep therefore seems to have evolved for energy conservation, supporting the theory. 
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Chest 2001

Found a positive correlation between insomnia and sleep apnoea, suggesting a link between the conditions.

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Morrell 2000

  • Found that up to 20% of older adults have the condition which is ten times more than in younger adults, though the disorder is considered to be more severe in the young. 
  • Doctors report increasing numbers of young people with insomnia and sleep apnoea, this may be linked to obesity in the young. 
  • It is though that this difference is due to physical changes in the Cardiovascular System as people age. 
  • One implication is that different forms of treatment may be required for people of different ages, although adressing obesity may be the best way forward.
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Stickgold 2009

  • Insomnia causes depression
  • It was found that apnoeic insomniacs had twice the rate of depression in comparison the the genral population. 
  • Suggests that the best way to treat such mental disorders is to alleviate apnoea and insomnia.
  • However, Horne 2009 points ot that this claim is not proven and is more probable. He also beleives that obesity is more responsible for rises in depression levels.
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Lundh et al 1995

  • Personality tested 233 persistant insomnia patients and found that sufferers had high scores on anxiety, low scores on self-esteem and were over-dependant on others.
  • Effects of these factors are difficulty regaining lost sleep, daytime sleepiness and lack of concerntration.
  • Supports the idea that personality plays a role is causing and maintaining insomnia.
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Kales et al 1976

  • Personality tested 124 insomniacs and found taht 85% were more likely to internalise psychological problems, this was not the case in a control group.
  • They proposed that the internalisation leads to a constantly higher levels of emotional arousal. Also leading to to higher level of physical arousal, high heart rate and temperature. This means more difficulty sleeping and increased likelyhood of anxiety which is a risk factor in insomnia.
  • This supports Lundh's findings that a psychological mechanism may be responsible for insomnia. 
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De Carvalho et al 2003 & Grano et al 2006

De Carvelho et al 2003

  • Studied 32 Brazilian insomniac patients and found high levels of anxiety and insecurity in female patients.

Grano et al 2006

  • Found that male insomniacs tend be impulsive characters.

This implies that male and female sufferers of insomnia are affected by different personality traits.

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Montplaisir 2007

  • Tested 16 patients with narcolepsy and cataplexy and found that they had a higher percentage of REM sleep although this may be a cause or an effect of the condition.
  • It has been observed that when people with narcolepsy fall asleep they move straight into REM sleep rather than moving through the normal stages of sleep. 
  • This can explain their rapid loss of muscle control (cataplexy) found in REM sleep and the intrusion of REM type sleep (hallucinations) into daytime sleep.
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Mignot et al 1998

  • Found a 30% concordance rate for narcolepsy in Mono-zygotic twins (identical), suggesting a genetic link.
  • However this rate is fairly low so environmental factors must be important (diathesis stress model).
  • Human narcolepsy does not run in families and further research has suggested that human narcolepsy is unlikely to just be caused by genes. 
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Daniels et al 2001

  • Gave questionnaires to 500 patients of the Narcolepsy Association.
  • Found that they had lower energy/vitality levels, reduced social functioning and lower levels of physical activity.
  • 57% were depressed
  • The condition put limitation upon their education, work, home and social life. 
  • This demonstrates the extensive impact of the disorder on health-related quality of life. 
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Broughton 1999

  • Reported that symptoms of narcolepsy cannot be cured at present but can be controlled with behavioural treatments and medication. Stimulants combat daytime drowsiness while cataplexy is addressed with anti-depressants.
  • However, drugs only reduce symptoms at best.
  • Lifestyle adjustments such as regulated sleep schedules and non-exitatory activities before bedtime are more successful. 
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Broughton 1968

  • Sleepwalking tends to run in families
  • Found that sufferers are 10 times more likely to have a close relative with the disorder tahn the general public.
  • Tis suggests a genetic factor.
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Lecenfreux et al 2003

  • Found a higher incidence amoung MZ twins rather than DZ twins 50% compared to 12% which suggests a genetic link.
  • However, MZ twins also tend to have identical environments which could be a confounding variable.
  • The identification of genes associated with the disorder does not mean that there is a definate genetic cause.
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Zadra et al 2008

  • Showed experimentadly that sleep deprivation can trigger sleep walking. Observed 40 patients in sleep labs during one normal nights sleep.
  • 50% showed signs of sleepwalking. 
  • On the second night the patients were prevented from falling asleep for 25 hours, then allowed to sleep. Sleepwalking rose to 90%.
  • Sleep deprivation does not lead to sleepwalking in normal individuals. Only appears to happen in individuals genetically predisposed to sleep walking.
  • This may provide a way of diagnosing the condition in vulnerable people. 
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