Unit 3: Biological rhythms and sleep Exam board specification

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Unit 3: Biological rhythms and sleep
Exam board specification:

Biological rhythms

  • Circadian, infradian, and ultradian rhthyms, including the role of endogenous pacemakers and of exogenous zeitgebers in the control of circadian rhythms

  • Disruption of biological rhythms, for example shift work, jet lag


  • The nature of sleep including stages of sleep and lifespan changes in sleep

  • Functions of sleep, including evolutionary and restoration explanations

Sleep disorders

  • Explanations for sleep disorders, including insomnia, sleep walking and narcolepsy

What you need to know:
You will be expected to outline and evaluate each of the areas.

Circadian rhythms:

  • The sleep-wake cycle, including the role of enodogenous pacemakers and endogenous zeitgebers in this rhythm.

Disruption of the biological rhythms:

  • How circadian rhythms are affected by shift work and jet lag.

Infradian rhythms:

  • The menstrual cycle.

Ultradian rhythms:

  • The sleep cycle.

Nature of sleep:

  • The sleep stages

  • The changes in sleep patterns throughout a person’s life.

Functions of sleep:

  • Evolutionary: Webb & Meddis

  • Restoration: Horne & Oswald

Explanations for sleep disorders, including insomnia, sleep walking and narcolepsy:

  • Primary Insomnia: Predisposing, precipitating and perpetuating factors

  • Sleep walking: Diathesis-stress model

  • Narcolepsy: The role of hypocretin

Key terms/concepts

Where possible, include examples in order to help your understanding (see example)

Circadian rhythms

These are rhythms that last 24 hours. E.G. the sleep-wake cycle.

Our bodies have many other circadian rhythms, such as temperature regulation and bowel regulation.

Endogenous pacemakers

Exogenous zeitgebers

Suprachiasmatic nucleus (SCN)


Jet lag

Phase delay

Phase advance

Social jet lag

Shift work

Infradian rhythms

Follicle stimulating hormone


Luteinizing hormone




Ultradian rhythms

REM sleep




Here are a few extra boxes if you come across any additional terms:

Biological rhythms

Circadian rhythms
Circadian rhythms are biological rhythms that last about 24 hours, that is, one day in length. One example is the sleep-wake cycle. This cycle is controlled by endogenous pacemakers acting as internal body clocks that elicit internal biological changes such as the secretion or inhibition of hormones, and exogenous zeitgebers that serve to entrain our biological clocks.
An example of an endogenous pacemaker is the suprachiasmatic nucleus (SCN) which has neural connections with the pineal gland, responsible for producing melatonin. An increased production of melatonin leads to increased tiredness.

There are many exogenous zeitgebers, one being light. The retina has photosensitive cells that send signals to the optic chiasm which in turn stimulates the SCN. When it is lighter, the SCN tells the pineal gland to produce less melatonin thus making us feel more awake. In this sense, internal and external pacemakers work together to control our sleep-wake circadian rhythm.

It is thought that out natural, innate clock runs just over 24 hours.
Another example is body temperature, which is regulated by an endogenous pacemaker in the suprachiasmatic nucleus. Core body temperature changes by about 1 degree Celsius. Temperature is higher in the afternoon than in the morning. During a night’s sleep, core body temperature declines gradually. The rhythm is associated with the circadian rhythm of the sleep-wake cycle. We feel sleepier when the body temperature is low.

Evaluation of circadian rhythms - the sleep-wake cycle

Research evidence:

Morgan (1995) used hamsters with abnormal circadian rhythms (20 hrs rhythm rather than 24) and transplanted SCN neurons from these hamsters into normal hamsters (24hr rhythm). They found that the normal hamster’s circadian rhythms changed from 24hrs to 20. They also did this experiment in reverse by transplanting the SCN neurons from the normal hamsters to the abnormal hamsters and found their circadian rhythm changed from 20hrs to 24.

How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?

Schochat et al (1997) studied the role of melatonin in circadian rhythms. Six male participants spent 29 consecutive hours (from 7 am one day to noon the next) in a sleep laboratory. They had to spend 7 minutes in every 20 minutes lying down in a dark room trying to sleep. The researchers were looking at how easy/hard the participants found it to go to sleep; the period that is the easiest for people to go to sleep in is known as the sleep gate. Blood samples were also taken every 20 minutes to allow the measurement of melatonin. The researchers found that the daily secretion (release) of melatonin into the blood consistently preceded the sleep gate by 100-120 minutes. Other researchers have also found that people who suffer from insomnia (sleeplessness) found it much easier to get to sleep when they were given melatonin about 2 hours before bedtime.

How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?

Michel Siffre spent 2 months living in a dark cave. He developed a 25 hour sleep wake cycle when it is normally 24 hours. Miles et al (1977) wrote about a man who was blind from birth. He had a 24.9 hours circadian rhythm despite the fact that he was exposed to external cues such as radios and clocks. The only way he could reset his circadian rhythm to 24 hours was through the use of sedatives to help him sleep and stimulants to help him wake.

How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?

Mariana Figeuiro (2012) set out to determine what the effects of self-luminous tablets (Ipads) might be on melatonin suppression. They observed and gathered data on 13 volunteers who used the devices to watch films, play games and read documents. They found that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent. Stimulating the human circadian system to this level may affect sleep in those using the devices prior to bedtime.

How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?


Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.

Wider evaluation points:

Individual differences:

  • Czeisler et al (1999) found that circadian cycles in different people can vary from 13 to 65 hours.

  • Cycle onset varies, Duffy et al. (2000) found that morning people prefer to rise early and go to bed early (about 6.00 am and 10.00 pm), whereas evening people prefer to wake and go to bed later (10.00 am and 1.00 am).

Usefulness/Practical applications:

  • Implications surrounding use of self-luminous tablets.

  • Chronotherapeutics is the study of how timing (chronos) affects drug treatments (therapy). Since the circadian rhythm affects digestion, heart rate, hormone secretions and other functions, this should be taken into account when taking drugs. For example, medications that act on certain hormones may have no effect if taken when target hormone levels are low but are fully effective if taken when levels are high.

  • Another application of this research is when deciding on the best time to study. You are most alert in the morning and early evening, so those are the best times to work.

Ultradian rhythms
Ultradian rhythms are rhythms that last less than a day such as the sleep cycle.
There are two main phases of sleep which make up the rhythm; REM (rapid eye movement) and NREM (non-rapid eye movement). These can be observed on an electroencephalogram (EEG).

NREM sleep has 4 stages, stage 1 and 2 are known as the lighter stages of sleep and stage 3 and 4 are known as slow wave sleep (SWS). Most people have five cycles of sleep that last approximately 90 minutes. Deep sleep, or slow-wave sleep (SWS), occurs in only the first two cycles; REM sleep occurs in all of the cycles, and increases during the course of the night’s sleep.

  • First cycle: Go down the sleep staircase from stage 1 to 4; then ascend through stage 3 and then stage 2. Stage 5, or REM sleep, follows this and lasts for approximately 10 minutes.

  • Second cycle: Begin at stage 2, which lasts for about 20 minutes, then descend through stage 3 to the deep sleep of stage 4, which lasts approximately 30 minutes. Then ascend through stages 3 and 2. REM sleep (stage 5) completes the cycle and again lasts for about 10 minutes.

  • Third cycle: Enter at stage 2 and spend about an hour in this stage. Next we miss the descent of the sleep staircase by going straight into REM sleep (stage 5) for approximately 40 minutes.

  • Fourth cycle: Enter at stage 2 for 70 minutes and then enter REM sleep (stage 5) for approximately an hour.

  • Fifth cycle: Enter at stage 2 followed by REM sleep (stage 5). This is known as the emergent cycle because we may wake from either stage. We are more likely to remember our dream if we wake in stage 5 and can experience a hypnogogic state again and so recall vivid visual images as we wake.

Another example of an ultradian rhythm is the levels of alertness throughout the day. Studies have shown that we have stages of alertness throughout the day. A study of pupillary size showed that these rhythms can last around 75-125 minutes and could be dependent on melatonin levels or central nervous system arousal. Studies have generally shown that humans tend to be most alert at two separate times in the day, in the morning just after waking up, and at around 7-8 pm.

Evaluation of ultradian rhythms – the sleep cycle

Research evidence:

There is much evidence concerning the ultradian rhythm – the main body of research has been carried out in sleep labs using specialized equipment which the sleeper is wired up to:

  • Electroencephalographs (EEGs) measure electrical activity (brain waves)

  • Electro-oculograms (EOGs) measure eye movements

  • Electromyograms (EMGs) measure muscle movement

This equipment has allowed researchers to distinguish the stages of sleep and to identify the cycles of sleep.

Dement and Kleitman (1957) studied 9 participants in a sleep lab using the equipment mentioned above. They found that the participants all showed similar rhythms whilst sleeping which alternated between NREM and REM. REM lasted from 3 to 50 minutes and the REM periods occurred at regular intervals during the night. The mean period between each REM phase for the whole group was 92 minutes, with individual norms varying between 70 minutes and 104 minutes.

How does this evidence demonstrate ultradian rhythms?

Wehr (1992) conducted a study in which participants (young adults) were plunged into darkness for 14 hours per day. Whilst it took some time for their sleep to regulate, by the fourth week the participants settled into a regular pattern: they slept first for three to five hours, and then woke for one or two hours before falling into a second three to five hour sleep.
Ekirch (2001) has carried out much research into the historical record across cultures, and has found substantial evidence for the segmented sleep pattern observed by Wehr, although in western society the idea of a first and second sleep had vanished by 1920. It seems that as the night has become more of a time for social activity, the length of time that people wish to spend on rest has reduced, so the gap between the first and second sleep becomes a waste of time and people now attempt to sleep in one eight hour segment.

What does this research suggest about biological rhythms?


Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.

Wider evaluation:

Individual differences:
How does Dement and Kleitman’s study demonstrate individual differences in the sleep cycle?

In what way do ultradian rhythms differ with age? (you may need to look at the ‘lifespan changes in sleep’ section)

Infradian rhythms
Infradian rhythms are biological rhythms that last longer than a day. An example would be the menstrual cycle, which on average is 28 days. It is controlled endogenously by hormones such as oestrogen, follicle stimulating hormone (FSH) and luteinising hormone (LH). The pituitary gland produces FSH which starts the development of one egg in a follicle in one of the ovaries stimulating the ovaries to produce oestrogen. This stimulates the pituitary gland to secrete LH which causes ovulation and stimulates the empty follicle to produce progesterone. Progesterone causes the lining of the uterus to get thicker ready for the fertilised egg. If the egg is not fertilised, production of oestrogen and progesterone stops, the lining of the uterus breaks down and menstruation occurs.
It is now thought by some researchers that the occurrence of any single menstrual cycle could be influenced by prolonged exposure to other women who release pheromones during menses causing inter-woman menstrual synchronisation. Pheromones are biochemicals, like hormones and neurotransmitters, but instead of being transmitted through the blood or brain cells, they are released into the air, and affect other individuals. In humans, they can be released in sweat.
Another example is seasonal affective disorder. Sufferers of SAD feel depressed in the winter months. The cycle occurs annually. The longer nights in winter mean that we experience longer periods of darkness. Melatonin is produced in dark conditions and has been associated with depression.
Evaluation of infradian rhythms – the menstrual cycle

Research evidence:

Russell et al (1980) arranged to apply the pheromones of one woman to a group of sexually inactive women. The donor’s odour was collected from pads placed under her arms. Once every 24 hours the pads were replaced. The old pad was then dissolved in alcohol to remove any bacteria. Finally, the pad was rubbed on the upper lip of each participant. This was repeated daily for 5 months. Some of the women were in a control group where they received the same treatment but did not receive the odour. Participants did not know which group they were in. A record was kept of the participants’ menstrual cycles. At the end of the experiment, four out of five women in the odour group had menstrual cycles that synchronised to within a day of the odour donor.

McClintock (1971) suggested that male pheromones may reset a woman’s biological clock. This comes from the observation that women who work with men often experience a shortening of their menstrual cycle. This would be an evolutionary advantage because females who reproduce more often will have more offspring and therefore their genetic line is likely to become dominant

How does the evidence above demonstrate the role of exogenous zeitgebers in this rhythm?

Reinerg (1967) documented the case of a woman who spent 3 months in a cave with only dim lighting and found that her menstrual cycle became shorter (25.7 days)

How does this evidence demonstrate the role of endogenous pacemakers in this rhythm?


Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.

Wider evaluation points:

Disruption of biological rhythms: jet lag and shift work

You are going to look at how circadian rhythms, in particular, are disrupted by jet lag and shift work.

Jet lag

Jet lag occurs when normal circadian rhythms are disrupted by travelling across time zones. When an individual travels across time zones there is a shift in zeitgebers, which causes a temporary mismatch between our internal circadian clock and external cues (e.g. light and time). Therefore disruption occurs when there is sufficient discrepancy between internal time (your biological clock, which is set to British time) and external time (local time of destination).

Travelling from east to west leads to phase delay of the body clock, which seems easier for the body to cope with than phase advance. Phase delay simply means extending the duration of a rhythm’s cycle (e.g. from 24 hours to 29 hours before returning to 24 hours again), whereas phase advance means shortening the rhythm’s cycle.
Typical effects of jet lag include: disturbed sleep, impaired functioning and decreased alertness.
Research on jet lag:
Schwartz et al (1995) analysed the results of American baseball games where teams had to travel across time zones to play opposing teams on the east or west coast, causing a time difference of three hours. West coast teams who travelled east had significantly fewer wins than the east coast teams who travelled west.
Klein et al (1972) confirmed the view that flying west to east caused more jet lag than flying east to west by looking at flights from the UK from the US. They also found that one day per time zone crossed (each time zone is one hour) was needed for full recovery
Cho (2001) studied the long term effects of travelling across time zones. Air crew regularly flying over 7 time zones with little turn-around time were found to have significantly higher levels of cortisol (a stress hormone) than those on short flights. The level of cortisol was associated with deficits in memory and spatial learning, although it may take five years before the effects are seen.

Shift work

Shift work is work that takes place on a schedule outside the traditional 9 am – 5 pm day. It can involve evening or night shifts, early morning shifts, and rotating shifts. Many industries rely heavily on shift work, and millions of people work in jobs that require shift schedules.

Shift work disrupts our circadian rhythms due to the constant change in shift patterns which means that our internal clock cannot adjust, this leads to an inconsistent sleep-wake cycle. Also, if the shift pattern involves night work this can cause disruption to the circadian rhythm because the individual is working when the body wants to be asleep and trying to sleep when the body wants to be awake.
Typical effects of shift work include: increased risk of cardiovascular disease, increased risk of gastrointestinal problems, e.g. constipation, higher risk of motor vehicle accidents and work-related accidents and probable increased risk of cancer, particularly breast cancer.
Research on shift work:

Knutsson et al (1986) found that individuals who worked shifts for more than 15 years were three times more likely to develop heart disease than non-shift workers.
Hansen et al’s (2012) study of 692 women from the Danish military found a link between the two. Hansen still found that working night shifts was associated with a 40% increase in breast cancer risk. The more nights shifts worked, the greater the risk of breast cancer. Hansen also found that shift workers who described themselves as being “morning” people — that is, they preferred to wake up early, rather than stay up late at night — had a four times higher risk of breast cancer than women who worked during the day. However Fritschi (2012) An Australian study of 1000 women showed no link between breast cancer and shift work.
Burch et al. (2005) found that night workers’ melatonin levels (measured in their urine) and sleep patterns were disrupted compared with day workers’. The night workers’ melatonin levels were too high, making them sleepy and prone to accidents.

Evaluation of disruption to biological rhythms

Consideration of the research evidence:

What does the research tell us about the effects of disrupting biological rhythms?


Write an IDA comment on how this point relates to the topic and why it is an important point.

Wider evaluation points:

Individual differences:

  • The effects of disrupting circadian rhythms vary between individuals.

Practical applications:

Jet lag:

  • Consuming melatonin may help resynchronise the sleep-wake cycle more quickly. Beaumont et al (2004) found that taking melatonin at bed time for 3 days before travel and 5 days after significantly reduced the symptoms of jet lag

  • Exposure to light can affect circadian rhythms. Burgess et al (2003) investigated if jet lag could be prevented by phase shifting (advance or delay) before travelling. They found that after three days of light exposure in the morning, the participants’ circadian rhythms shifted by an average of 2.1 hours. This means they would feel less jet lagged, and would be fully adjusted to the new time zone around two days earlier.

Shift work:

  • The research can help both those planning work schedules and workers. Czeisler et al (1982) proposed that it would be better to rotate shifts forward in time so one begins with a day shift, progresses to an evening shift and then turns to a night shift. They found that workers reported feeling better and much less tired on the job. The management reported increased productivity and fewer errors.

  • Dawson & Campbell (1991) found that workers exposed to a 4-hour pulse of bright light showed improvements in work performance. This shows that light acts as an exogenous zeitgeber in maintaining the rhythm of the SCN. Consequently, bright light has been used as a substitute for sunlight to reset the SCN.


The nature of sleep

Stages of sleep
Go to http://www.psych205.com/stages-of-sleep.html : Read the information and go through the PowerPoint presentation making notes in the spaces below











Evaluation of the stages of sleep

Research evidence:

Look through your pack and find three pieces of evidence that either tell you how the stages of sleep have been investigated or tell you something specific about the purpose of a stage of sleep.

Evidence 1

What does this piece of evidence show us about the stages of sleep?

Evidence 2

What does this piece of evidence show us about the stages of sleep?

Evidence 3

What does this piece of evidence show us about the stages of sleep?


Write an IDA point and comment on how this point relates to the topic and why it is an important point.

Wider evaluation points:

Additional IDA:

This area demonstrates how psychology can be considered scientific.

In the space below, elaborate on this statement and explain why this is important.

The nature of sleep
Lifespan changes in sleep
Premature babies:
REM sleep accounts for 80% of total sleep

  • REM sleep accounts for 50-60% of total sleep.

  • They sleep about 16 hours a day, but not in one continuous block, they tend to wake up every hour or so.

  • The sleep cycle is shorter than 90 minutes

  • They have immature versions of SWS and REM known as ‘quiet sleep’ and ‘active sleep’

  • They enter deep sleep through an initial period of light sleep that lasts for 20 minutes or more

  • By the age of 6 months a circadian rhythm has become established

  • By the age of one year they are usually sleeping mostly at night. The periods of deep sleep lengthen and there is a reduction in REM

Older children

  • REM sleep accounts for 25% of total sleep

  • At age 5, they sleep for about 12 hours a day, although this does vary from child to child – some need more sleep than others.

  • Parasomnias (sleep disorders) such as sleep walking and night terrors are common

  • The need for sleep decreased during this stage


  • REM sleep accounts for 20% of total sleep

  • The need for sleep increase slightly at this stage to about 9 or 10 hours a night

  • The experience phase delay – this means they feel naturally more awake later at night and have more difficulty getting up early

  • REM sleep in males is sometimes accompanied by orgasm and ejaculation


  • They typically sleep for around 8 hours a night

  • 25% of sleep is spent in REM

  • Sleep disorders such as insomnia are more likely

People in their 60s

  • 50% reduction in stage 3 & 4 sleep

  • REM accounts for about 20% of sleep

  • Getting to sleep becomes more difficult and they are more likely to wake up during the night

  • Daytime naps are more likely

  • They experience phase advance where they feel sleepier earlier in the evening and wake up earlier

People in their 70s & 80s:
REM sleep accounts for 10% of total sleep
People in their 90s:
No stage 3 or 4 sleep
Evaluation of lifespan changes in sleep

Research evidence:

Ohayon et al. (2004) carried out a meta-analysis of 65 studies that represented 3577 participants aged 5 to 102. The analysis showed that total sleep decreased from childhood to adolescence but only on school days. Deep (slow-wave) sleep was negatively correlated with age. In adults, total amount of sleep, percentage of slow-wave sleep and the percentage of REM sleep all decreased with age. The percentage of stage 1 and stage 2 sleep increased with age.

What does this piece of evidence tell us about the lifespan changes in sleep?

Kelley et al. (2014) reviewed research into circadian rhythms and sleep in relation to adolescents. They suggest that waking at 7.00 for older adolescents is like a 4.30 start for a teacher in their 50s. Adolescents are too alert in the evening to fall asleep as their circadian clock shifts to a later time. Some research indicates this may be a result of hormone changes. The mismatch between the biological drive to sleep and wake at a later time clashes with the requirement to get up early, which can result in sleep deprivation, which has a negative effect on cognition as well as on emotional and physical health. Kelley and Lockley (2013) found that test performance was significantly higher at 2 in the afternoon than at 10 in the morning.

What does this piece of evidence tell us about the lifespan changes in sleep?

Wolfson and Carskadon (1998) surveyed 3000 American high school students (equivalent of 6th formers) and found that they were on average getting 7.3 hours sleep and a quarter were getting 6.5 hours or less. They also found that those who achieved mostly A’s went to bed earlier and slept on average an hour longer each night than those getting lower grades.

What does this piece of evidence tell us about the lifespan changes in sleep?


Write an IDA point and comment on how this point relates to the topic and why it is an important point.

Wider evaluation points:

Usefulness/Practical applications

How do you think we could apply this research to everyday life?

Why do you think the research into lifespan changes is useful for Psychology?

Cultural differences:

  • Tynjälä et al. (1993) surveyed 11–16-year-olds from 11 European countries; altogether over 40,000 children responded. Israeli children slept least (average of about 8.5 hours) and Swiss children slept most (average of about 9.5 hours). In Korea mean sleep time was recorded as about 6.5 hours for adolescents (Shin et al., 2003) and a recent study in Iran found a mean time of 7.7 hours (Ghanizadeh et al., 2008), both supporting the view that sleep duration is shorter in Asia than Europe.

Functions of sleep
Restoration explanations
Oswald (1980) proposed an early restoration theory. He argued that REM sleep allows the restoration of and reorganisation of the nervous system. NREM sleep involves the restoration and repair of the body through release of growth hormone. Growth hormone is released from the pituitary gland in small bursts throughout the day, but it is released in larger amounts during stage 4 sleep. So, stage 4 sleep is particularly necessary to the repair of the body, and therefore plays a part in maintaining our physical health.
Horne (1988) said that sleep was needed for psychological recovery. He also recognised that not all sleep is equally beneficial. He distinguished between core sleep (stage 4 and stage 5/REM) and optional sleep (stages 1-3). He argued that core sleep is critical for normal brain functioning because during these stages the brain restores itself after the activities of the day, replenishing levels of neurotransmitters that help to keep us functioning well psychologically. This means that without a sufficient amount of sleep, our psychological functioning would be impaired.

Evaluation of restoration explanations


Choose an IDA point and write a comment on how the point relates to this topic and why this is an important point.

Research evidence:

Sleep deprivation evidence
Fill out the boxes explaining whether the sleep deprivation evidence lends any support to the theory and/or whether it challenges the theory in any way.


Which restoration theory it supports and why

Peter Tripp

Randy Gardner

Michael Cork – fatal familial insomnia

Dement (1960) compared participants who had been deprived of REM sleep with a control group who had been deprived of the same amount of NREM sleep. He found that the REM deprived group were more irritable, more aggressive and unable to concentrate on various tasks.
Borbely (1986) found that REM deprived individuals made 31 attempts to re-enter REM on the first night of deprivation, 51 attempts on the second night and over 60 attempts on the third
Sharpio et al (1981) found that runners who had taken part in an ultra marathon covering 57 miles slept about an hour and a half longer than normal on the two nights following the marathon. In addition, there was a much larger proportion of time devoted to stage 4 sleep.
Empson (1989) noted that the disruption of stage 4 sleep in healthy people resulted in stiffness in the back and muscle pain.

Wider evaluation points:

Functions of sleep

Evolutionary explanations

Evolutionary theories in general suggest that sleep evolved because it allows an organism a greater chance of survival in a hostile environment.

Webb (1974) suggests that sleep has evolved because it forces the animal to conserve energy. In general, animals that conserve energy are more likely to survive than animals that do not. Therefore, the characteristic that helps them conserve energy is more likely to be passed on to the next generation. Sleep helps animals conserve energy in a number of ways.

For example:

  • During sleep, behavioural activity stops, meaning less energy is spent on movement.

  • Body temperature and metabolic rate slow down, again, saving energy.

According to Webb, an animal’s sleep patterns will be determined by the rate at which it loses heat, what it eats and the availability of food. By comparing the sleep patterns of different species at different times, it is possible to see whether these factors appear to have an effect.

General information on animal behaviour:

  • The smaller an animal is, the faster it loses heat.

  • An animal’s diet determines its rate of energy intake and this in turn determines how long it must spend each day searching for food. Herbivores, such as cows and horses, eat food which is relatively poor in nutrients so must spend a great deal of time eating. Carnivores, on the other hand, such as cats and dogs eat food that is high in nutrients and so do not need to eat continuously.

  • Hibernation theory would predict that sleep time should increase when food is scarce, because the animal has a greater need to conserve energy.

Meddis (1975)

Moving around increases the chance of being noticed by predators so sleep allows for predator avoidance. Staying still is not easy. It is also more dangerous when it is dark, particularly if night vision is poor. The best solution would be to sleep. Animals that sleep during the day tend to hunt at night, which gives them an evolutionary advantage. For example,

Foraging requirements are also important. Grazing animals need to eat frequently, which is potentially dangerous because they cannot keep still or sleep while they need to eat. Therefore sleep would not be adaptive for them. He also suggested that sleep is a way to waste time when there is nothing better to do.
Evaluation of evolutionary explanations


Write an IDA point and comment on how this point relates to the topic and why it is an important point.

Research evidence

Bats, voles and other small mammals sleep for as many as 20 hours in every 24, whilst giraffes sleep for as little as 1 hour.

Lions sleep for as many as 18 hours a day, possible more if they have just made a large kill. On the other hand, horses sleep for only 3 hours in every 24.

Which theory does this evidence support and why?

Alison and Cicchetti (1976) analysed the sleep patterns of 39 animal species and found a relationship between risk of predation and amount of sleep. Animals with a high risk of predation slept less than those with a lower risk.

Which theory does this evidence link to? Explain whether this evidence supports or challenges the theory.

Sleep deprivation studies

How do the sleep deprivation studies challenge the evolutionary explanations of sleep?

Wider evaluation points:

General strengths and weaknesses:

  • Young (2008) reports that out of 5000 mammal species we have information about the sleep patterns of less than 150.

Why is this a problem?

  • The theory doesn’t explain why sleep is universal. All mammals sleep and some have evolved peculiar sleep patterns (dolphins sleep one hemisphere at a time).

Why is this problematic for the evolutionary explanations?

  • These explanations do not sufficiently explain the function of sleep for humans

Elaborate on this (why is this the case and why does this matter?)

Sleep disorders


A fairly new theory links narcolepsy, genes and the neurotransmitter hypocretin.

Hypocretin (also called orexin) is a neurotransmitter that regulates arousal, wakefulness, and appetite. The brain contains very few cells that produce orexin: in a human brain, about 10,000 to 20,000 neurons in the hypothalamus.
Some genetic variations on chromosome 6 (known as the HLA complex) predispose an individual to narcolepsy. These variations increase the risk of an auto-immune response to neurons in the brain that produce the neurotransmitter hypocretin (also known as orexin).
Hence people with narcolepsy often have vastly reduced numbers of neurons in their brain that produce hypocretin, because the cells that produce it have been destroyed by the auto-immune response.
It is also possible that for some people the auto-immune response is not caused by genes but by a flu vaccination.
Evaluation of narcolepsy explanation:

IDA points relevant to this topic:

Write an IDA point and comment on how this debate relates to the explanation and why this is an important point.

Research evidence:

Siegel et al (2000) managed to acquire the preserved brains of 4 narcoleptics and after a close examination they were found to have 93% fewer hypocretin neurons than a non-narcoleptic’s brain.

Mignot et al. (1999) found that narcoleptic dogs had a defective hypocretin receptor 2 gene, the hypocretin receptor 2 gene is found in both humans and dogs.

Broughton (1999) reported that lifestyle adjustments, such as regulated sleep schedules and relaxing before bed, were more successful at treating the symptoms of narcolepsy than drugs

Wider evaluation points:

Primary Insomnia

Speilman and Glovinsky (1991) said that predisposing, precipitating and perpetuating factors explain primary insomnia.

Predisposing factors include a genetic vulnerability to insomnia and the physiological state of hyperarousal. Hyperarousal is high physiological arousal when awake or asleep and it makes it more difficult for the individual to fall asleep.
Precipitating factors include stress or environmental change that may temporarily make it difficult to get to sleep. Environmental change includes changing time zones. Females suffer more from primary insomnia, as do older people so both of these factors count as precipitating factors.
Perpetuating factors maintain insomnia when the precipitating factors have gone. They include being tense when going to sleep or the expectation of poor sleep. These perpetuating factors are key to chronic primary insomnia.


Research evidence:

Nofzinger et al (2004) found that the transition from being awake to being asleep is usually associated with a decrease in activity in the brain stem, thalamus and prefrontal cortex. Using PET scans, Nolfzinger et al showed that insomniacs experienced a smaller decline in such activity when going to sleep. In fact, they found elevated level of activity in the brains of insomniacs.
Bastien et al. (2004) found that 60% of patients with insomnia could identify a trigger for their sleep disturbance, and these tended to be around family, work/school and health.
Ohayon & Roth (2003) Interviewed 14,195 participants representative of the general populations of the UK, Italy, Portugal and Germany over the telephone about their psychiatric history and their sleep patterns. They found that people with insomnia were six times more likely to report a mental health problem, such as depression or anxiety, than people without insomnia.

Wider evaluation points:

Sleep walking

A diathesis-stress model recognises that there are predisposing factors (the diathesis) and environmental causes to a disorder (the stress). It is important to realise that sleepwalking occurs in SWS.

This model of sleepwalking says that there is a genetic predisposition to sleep walking, which is the diathesis; this genetic predisposition is likely to be incomplete arousal – so people’s genes predispose them to be in this state, which is a state between sleep and wakefulness. Sleepwalking occurs in SWS and typical EEG recordings taken during sleepwalking show delta waves typical of SWS plus higher frequency beta waves which are characteristic of an awake state. Hence it appears that sleepwalking occurs when the person in SWS is awakened but the arousal of the brain is incomplete so they still appear asleep.
The stress (environmental) factors that make sleepwalking more likely to occur in those with a predisposition include sleep deprivation, drinking alcohol, fever and being a child. Children are thought to be more vulnerable because they have more SWS than adults and it’s thought that the mechanism that inhibits motor activity during SWS is not properly matured. Hormonal changes during puberty and menstruation may also be triggers for sleepwalking.


Research evidence:

Ohayon researched a sample of 19,136 individuals from 15 states of the U.S. The study showed that people with depression were 3.5 times more likely to sleepwalk than those without, and people with alcohol abuse/dependence or obsessive-compulsive disorder were also significantly more likely to have sleepwalking episodes.
Hublin et al (1997) Monozygotic (1045) and dizygotic (1899) twins were interviewed about their sleepwalking habits in childhood and adulthood. The study found that there was a link between genetics and sleepwalking.
Zadra et al (2008) investigated 40 patients and recorded sleepwalking for one baseline night and during recovery sleep after 25 hours of sleep deprivation. The results show that 32 episodes were recorded from 20 sleepwalkers (50%) at baseline whereas recovery sleep resulted in 92 episodes being recorded from 36 patients (90%).

Wider evaluation points:

Previous exam questions

January 2010
1 (a) Outline one example of a circadian rhythm (4 marks)

(b) (i) Outline one or more explanations for sleep disorders (eg insomnia, sleep walking, narcolepsy)

(4 marks)

(ii) Evaluate one or more explanations for sleep disorders. (16 marks)

June 2010

  1. Outline lifespan changes in sleep. (8 marks)

  2. Outline and evaluate one explanation for the functions of sleep. (16 marks)

January 2011
Discuss the role of endogenous pacemakers in the control of one biological rhythm. (8 marks + 16 marks)
June 2011

  1. Outline the nature of sleep. (8 marks)

  2. Consider the consequences of disrupting biological rhythms. (16 marks)

January 2012

  1. Outline one explanation for narcolepsy. (4 marks)

  2. Outline and evaluate one or more evolutionary explanations for the functions of sleep.

(4 marks+ 16 marks)
June 2012

  1. Outline one or more examples of ultradian rhythms. (4 marks)

  2. Outline and evaluate restoration explanations of the functions of sleep. (4 marks + 16 marks)

January 2013
Discuss explanations for insomnia and/or narcolepsy. (8 marks + 16 marks)
June 2013
Discuss research into the disruption of biological rhythms (eg shift work, jet lag). (8 marks + 16 marks)
June 2014

  1. Outline lifespan changes in sleep (4 marks)

  2. Outline and evaluate one or more restoration explanations for the functions of sleep (4 + 16 marks)

June 2015
Outline one explanation for narcolepsy. [4 marks]

Outline and evaluate evolutionary explanations for the functions of sleep. [4 marks + 16 marks]

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