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What techniques are used in sleep research?

What is an encephalograph and why is it used?

An EEG or an electroencephalograph; which is a recording of the electrical activity of the brain. Electrodes on the scalp pick up electrical activity from the millions of neurones in the brain. Different patterns of EEG activity can reflect different brain states, such as arousal and the stages of sleep.


EOG – Eye movements

EMG – muscle movement 

Desynchronised EEG – a reading that has no regular pattern of electrical activity. This is typically recorded when the brain is active

Synchronised EEG – a reading that has a regularpattern of electrical activity. Repeated waves with a particular amplitude and frequency

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NREM Sleep

As we move through the sleep stages from drowsiness to stage 4 our respiration, heart rate and blood pressure fall. Blood flow to the brain falls, showing it is becoming less active.

Stage 1:

  • Lasts about 15 minutes
  • Body relaxes and individual feels drowsy
  • EOG shows slow rolling eye movements
  • EMG shows reduction in muscle tension
  • Hallucinations may occur eg. Feeling of falling
  • Lightest stage of sleep so we are easily awakened

Stage 2:

  • Lasts about 20 minutes
  • K-complexes also occur which are responses to external stimuli eg noise
  • EOG shows little eye movement
  • EMG shows muscles are relaxed
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Stage 3

  • Lasts about 15 minutes
  • Also known as slow wave sleep (SWS) – EEG consists of large, slow delta waves
  • EOG and EMG same as in stage 2

Stage 4

  • Lasts about 30 minutes
  • Also known as slow wave sleep
  • EOG and EMG show little activity
  • The deepest stage of NREM to hard to be awakened
  • Body temp, heart rate and blood pressure drop to lowest and growth hormones secreted
  • Sleep talking/walking and night terrors 
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Rapid eye movement (REM) sleep

What did Dement and Kleitman (1957) discover when observing their EEG recordings in the sleep lab?

  • Lasts about 15 minutes in the 1st cycle and builds up to an hour by the 4th and 5th cycle
  • Rapid eye movement
  • EEG shows beta waves which also occur during a relaxed waking state
  • EMG shows the body is paralysed
  • Dreaming occurs
  • Hardest stage to be awakened from
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Evaluation of the sleep lab method


  • EEG, EOG, EMG’s provide objective measures of sleep (non bias)
  • A reliable scientific method as the EEG measures activity from outside the brain HOWEVER it cannot show exactly which areas are involved in each stage of sleep
  • Psychology as a science
  • Ethics -> using EEG is non invasive and painless therefore ethical


  • Sleep lab is an artificial condition and people are wired up to machines, validity may be limited because participants may not sleep naturally in the lab
  • The sleep lab is reductionist as it does not reflect many factors that can influence sleep in real life
  • Most people have 5 sleep cycles and sleep for around 8 hours. Many sleep less/more; Patterns of sleep may vary from each individual
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The Evolutionary Explanations of Sleep

These explanations suggest sleep has evolved into an essential behaviour because it provides selective advantages for the animals involved.

There are two main explanations:

1. Meddis (1975) – Predator-prey status

2. Webb (1982) – Hibernation theory

These explanations do not see sleep as serving a basic physiological function (i.e. sleep is not strictly necessary) but says it has other functions such as energy conservation, safety etc.  

They suggest sleep is basically a habit which animals have evolved to help them fit into their ecological niche (their lifestyle – how and where they live)

Different species have different sleep patterns and these have evolved depending on other aspects of their lifestyle for example: (next pages)

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Ecological Niche / Lifestyle factors

Environment e.g. aquatic or terrestrial:

  • Aquatic animals sleep differently to land animals e.g. dolphins sleep one side of the brain at a time (uni-hemespheric sleep)
  • All animals are either diurnal (day living) or nocturnal. This means that they are adapted to be active only in part of every 24 hours and for the remained they will be inactive

Predator or prey:

  • Is the animal a carnivorous predator or a herbivorous prey? Prey are more vulnerable than predators, especially when asleep

Sleep site:

  • Does the animal sleep in a relatively safe deep burrow or in a more exposed location for example on the African savannah


  • we have already seen that large animals tend to sleep less than smaller animals. Is this to do with lifestyle, or do large animals have a different physiology to small animals
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1. Meddis (1975): Predator-prey status

  • Sleep keeps vulnerable prey animals safe
  • Diurnal animals cannot forage food at night so sleep evolved to keep them safe
  • Animals at risk from predators would have evolved to sleep more- to stay safe
  • Sleep is affected by risk of danger and food gathering

2. Webb (1982): Hibernation theory

  • Hibernation and sleep are to conserve energy when foraging would be difficult or impossible
  • Animals are inactive when asleep which conserves energy
  • Animals with a high metabolic rate (therefore use more energy) will sleep more
  • Difficultly in food gathering and metabolic rate affect sleep
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Animals do vary in sleeping habits

Allison and Cicchetti (1976) studied sleep in 39 animal species and found that prey animals sleep for significantly less time than predators, opposing Meddis’s view that sleep keeps vulnerable prey animals safe.  However prey animals are often herbivores and therefore need to spend most of their time grazing which may explain why they sleep less (Lesku et al 2006).

The hibernation/energy conservation approach shows that the basal metabolic rate (BMR) is positively correlated with sleep time (the higher the BMR, the more the animal sleeps – to conserve energy)  Berger & Phillips (1995)

Small animals have a higher BMR than large animals, therefore sleep more.

  • Contradicts the Meddis view that sleep keeps vulnerable prey animals safe, although this may be because their sleep site has a bigger effect on the evolution of sleep (so still evolutionary; safe from prey)
  • Prey animals = herbivores, therefore they need to graze a lot, suggesting that evolution is still affecting sleep
  • Supports Webb, suggesting that sleep may have evolved to conserve energy
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sleep time and sleep patterns.

Lesku et al:

Analysed data on sleep patterns for 54 species.They studied a range of variables:

  • body mass, brain mass, BMR, sleep exposure, herbivore/carnivore)


  • Brain mass is positively correlated with REM
  • Sleep site negatively correlated with REM (more in danger, less REM because they are easily awakened and can be more alert when predators attack)
  • Herbivores have less REM than carnivores (carnivores less likely to be attacked than herbivores)


  • Sleep time and proportions of REM and NREM are influenced by a range of factors such as sleep sites, BMR and brain and body mass
  • This supports the evolutionary perspective because it shows how animals adapt to their environment and vulnerability 
  • Different animals sleep for different amounts of time because they have adapted to survive in their ecological niche
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  • This research was often based on observations of animals in their natural habitat and therefore has high external validity.
  • Subsequently this study can give us a good indication of the effects of evolution on sleep cycles.


  • Correlational evidence is a weakness because we are unable to establish cause and effect
  • Therefore this study may not show the effect of evolution on sleep cycles
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  • This research was often based on observations of animals in their natural habitat and therefore has high external validity.
  • Subsequently this study can give us a good indication of the effects of evolution on sleep cycles.


  • Correlational evidence is a weakness because we are unable to establish cause and effect
  • Therefore this study may not show the effect of evolution on sleep cycles
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Why hasn’t sleep been selected out

An argument against the view that sleep has an important adaptive function, is the fact that sleep is found in species that would seem to be better off without it.

Pilleri (1979) captured two Indus dolphins. These dolphins live in muddy waters of the Indus river in Pakistan and have evolved blindness because good eyesight is unnecessary in the poor visibility of their environment.  

They have an excellent sonar system which lets them find prey while dodging the debris carried by the river in the monsoon.  Despite the dangers of potential injury from floating debris, sleep has not disappeared. The dolphin sleeps in short naps of between 4- 60 seconds for a total of about 7 hours per day

Why is this complicated adaptation a problem for the evolutionary approach? If sleep were only adaptive then it would have been eliminated through natural selection.

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Pilleri Evaluation


  • Controlled conditions, high internal validity
  • can assess sleep patterns empirically(psychology as a science)
  • objective measuring
  • no extraneous variables therefore increasing support for the study that sleep is not adaptive


  • Dolphins may not show normal sleep patterns in captivity reducing the validity of this study therefore sleep may still be an adaptive approach in a real life scenario. 
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We have such a strong drive for sleep when we are

Michael Corke suffered from Fatal Familial Insomia; he didn’t sleep for 6 months and died of exhaustion which shows we need sleep.


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Evaluation of the Evolutionary Approach


It takes whole animal and its lifestyle into account, it considers a range of complicated factors to explain sleep behaviour, therefore it is not reductionist


The evolutionary explanation relies heavily on studies of non-human animals resulting in ethical issues

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Oswald's Restoration Theory

This approach claims that sleep is essential to our survival. It has an essential function in restoring the body and mind.

  • He noticed that people recovering from severe trauma to the brain, such as drug overdoses, spent more time in REM sleep
  • New skin cells grow more quickly during sleep
  • This is linked to the increased release of the body’s growth hormone during deep sleep
  • REM is essential for restoration of the brain
  • NREM is essential for the restoration of the body
  • Newborn babies spend a third of every day in REM sleep
  • This is because it is a time of massive growth, with the development of new synaptic connections between neurons requiring neuronal growth and the production of neurotransmitters
  • Brain energy consumption during REM is similar to waking behaviour.

The Main predictions of Restoration Theory are:

  • Deficits in functioning when sleep deprived
  • ‘rebound’ effects following sleep deprivation
  • Increase in REM sleep during brain growth, reorganisation and repair
  • Increase in SWS/NREM(slow wave sleep) during times of illness or injury
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Evaluation of the Restoration Theory – Studies and

1. Effects of physical exercise on sleep: 

If NREM has a physical restorative function, then you would expect an increase in it after excess physical exercise

Shapiro (1981) studied people who completed an ‘ultra marathon’, running 57 miles. They slept for an extra 1.5 hours for the 2 nights after the race and stage 4 sleep took up a greater proportion of their total sleep time than usual (usually approx 25% of sleep time, was approx 45% after the race). 

However, Ryback  & Lewis (1971) got healthy volunteers to spend 6 weeks resting in bed and found no change in their sleep patterns.

What do these studies suggest about the effects of physical exercise on sleep?

Shapiro 1981 supports the idea that stage 4 sleep necessary to restore the body

Ryback and Lewis HOWEVER restoration theory would predict less need for sleep especially during stage 4 if participants were not physically active – but this was not the case

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Strong support from sleep deprivation studies

Study 1: Peter Tripp

  • Stayed awake for 8 days for a charity/world record (201 hours).

What was he like before he did his study?

Nice, cheerful, upbeat, happy

Why were sleep deprivation studies not popular with psychologists in 1950s?

Soldiers got tortured through sleep deprivation and they saw the effects of long term sleep deprivation, they were changed men

What were the effects of short term effects of sleep deprivation?

Drop in body temperature, hallucinations, delusions, 90 minute REM cycle, don’t know what’s going on, enter altered state of consciousness, brainwaves showed he was asleep

What were the long term effects of sleep deprivation?

Got divorced afterwards, couldn’t recover centre of gravity, lost his job, no longer himself

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  • High internal validity, never left alone, always had someone with him
  • Had no time to recover/restore body brain so his body forced him into sleeping
  • Proves/suggests we need REM


  • Only one person, low population validity, hard to generalise
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Randy Gardner

  • Stayed awake for 11 days (264 hours).
  • Achieved world record for total sleep deprivation
  • He was a 17 year old student who was trying to win the San Diego Science fair. He was observed by Dementand colleague from 80 -264 hours of sleep deprivation. 
  • After 80 hours he was cheerful, happy and physically fit
  • Even after 10 days, he was able to beat Dement on every game of baseball at an amusement arcade. He spoke fluently when giving a press conference after 11 days sleep deprivation.
  • However, it was hard for the researchers to keep him awake between 3am and 7am –they had to play basketball with him or drive round with the radio on loud. 
  • Randy had some hallucinations (saw street sign as a person), and delusions, some disjointed thinking and a short attention span. Overall, Dement said Randy had no psychiatric problems.
  • After the study, Randy slept for 14 hrs, 40 mins, then got up and went to school. In total, he caught up about 24% of his missed sleep –but most of the missed REM and stage 4. 

Why does this study support Restoration theory?

Because he ‘caught up’ on his missed REM/Stage 4 afterward... some hallucinations etc – so supports the theory we need it. No long term detrimental effects 

Weaknesses of the study: Wasn’t monitored until 80 hours of sleep deprivation so could have slept during that time; Case study... low population validity... harder to generalise

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Evaluation of the Restoration Theory – Comparison

Horne’s Restoration theory

Horne proposed a similar theory to Oswald.  Sleep deprived participants could not complete cognitive tasks effectively indicating that sleep deprivation affects cognitive processes.

Only need core sleep -> stage 3&4&REM (disruption of sleep = cause problems)

Optional sleep -> stage 1&2 (disruption of sleep = no impact)

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Evaluation of the Restoration Theory


  • Psychology as a science – monitor sleep patterns with EEGs, EMGs and EOGs therefore objective as less affected as bias, more valid


  • Reductionist – the only reason or sleep isto restore functioning therefore simplifies a complex behaviour and cannot explain all the variations in sleep patterns between humans and animals (whereas evolutionary = non-reductionist)
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Further Support for Restoration Theory

Jouvet (1966) 

Jouvet kept cats on flowerpots over water. When they were in REM sleep, the cats flopped into the water (due to relaxation of head and neck muscles) and woke up. They then climbed back on to the flower pots. After a while, the cats became conditioned to wake up when they went into REM sleep, so they didn’t fall into the water so often


  • The cats exhibited bizarre behaviour (including hypersexuality)
  • Loss of control of body temperature
  • Eventually died after 35 days on average.


  • High internal validity


  • ethics; curel
  • animal research; can't generalise to humans
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Rechtschaffen used a yoked-control procedure to deprive rats of sleep in controlled way. He used pairs of rats:1 experimental, 1 control, which lived on a platform in plastic cages. The platform could rotate which would force the animals to take exercise to avoid falling in the water.

Experimental rats – platform began to rotate as soon as they fell asleep, therefore, sleep deprived.

Control rats– Same amount of rotations as experimental rat but not necessarily when asleep, therefore only slightly  sleep deprived. 


  • Control animals – perfect health
  • Experimental animals – after 7 – 10 days, became weak, uncoordinated, unkempt, developed sores that wouldn’t  heal on their bodies, lost body temperature regulation,  ate more food but lost weight – died after average 16 days, max 33 days.


  • High internal validity, lots of control
  • Suggests sleep is essential to function (supports theory..need to restore)


  • not ethical to harm animals
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Lifespan changes in sleep

As newborn babies, we spend a third of our time in REM sleep.

In old age, sleep patterns change again. Night time sleep becomes fragmented and shorter, due to a reduction in melatonin released, but this leads to sleepiness during the day and a tendency to nap. Having fulfilled some of their need for sleep during the day, the older person feels less tired at night and cannot fall, or cannot stay asleep. Older people also report more sleep disorders.

  • Large amounts of REM in newborns decreases over the first two years. Large amounts of REM can be explained by massive brain growth and the processing of large amounts of information.
  • Between the ages of 5 and 70 approximately 16% increase in stages 1&2 NREM and 60% decrease in deep NREM which is vital for efficient brain function.
  • Steady reduction of NREM from age 30 which implies the needs for these functions declines with age.
  • Older people with Alzheimer’s disease show a dramatic loss in deep NREM they also have problems with learning and memory supporting a link between deep NREM and normal cognitive processes.
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Evaluation of Lifespan Changes


  • Scientific – psychology as a science. Measure changes in sleep patterns using EEGS EOGs etc.. they are less subject to bias


  • Cannot tell us WHY these changes in sleep occur therefore it has little application purpose
  • Reductionist, cannot explain the full range of information (e.g. brain areas affect, reasons for changes etc) therefore it simplies a complex process
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