Biological Rhythms

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  • Created on: 01-09-15 15:00

Biological Rhythms


Periodic fluctuatoins in psysiological functioning. They are biologically driven. 

Types of Biological Rhythms:

  • Ultradian - Less than 24 hours
    • BRAC Cycle
    • Friedman and Fischer
    • Klien and Armitage
  • Circadian - 24 hours
    • Siffre
    • Wilkinson
    • Folkard
  • Infradian - More than 24 hours
    • Dalton
    • Russell Et Al
    • Hersey
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Ultradian Rhythms

Shorter than 24 hours. Most common example occurs during sleep - Sleep consists of 'cycles' = differing depths of conciousness each lasting 90 minutes

Freidman & Fisher (1967)

Held participants in luxurious isolation without any time cues, allowed them to help themselves to food, drink or cigarettes as they wanted. They found a rhythm in oral behaviour which waxed and waned every 90 minutes. 

Klien & Armitage (1979)

Tested participants performance on visual and spatial tasks. They found a 96 minute cycle which is the same as the sleep cycle at night. This means people perform better every 96 minutes

BRAC - Basic Rest Activity Cycle

We all have periods of attentivness during the day, this follows a 90 minute cycle. We can be really tired but once our friends have left we cant go to sleep because entered new cycle

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Circadian Rhythm

Repeated every 24 hours. E.g. The Sleep-Wake cycle.

Siffre (1975)

Spent 6 months in a cave with no time cues. Monitored, kept a record of bodily functions. At first his sleep-wake cycle was irregular but eventually setteled into one of 25 hours. Shows that even without time cues the body will naturally settle into a circadian rhythm. 

Folkard Et Al (1985)

Group of 12 in temporal isolation for 3 weeks. Deprived of time cues apart from one clock. At first the clock as normal but then it changed to one of 22 hours. Only one person's rhythm altered to the 22 hours, therefore the people had a STRONG INTERNAL CLOCK. This shows that even with misleading time cues sleep/wake cycle will stay the same.

Wilkinson (1968)

Tested navy reqruits on vigilance arithmatic and other criteria after different sleep scheduels. Found their performance peaked during mid-day which is when their temp was highest. This shows a 24 hour cycle as temp goes up and down. 

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Lasts longer than 24 hours. E.g. Menstral cycle occurs every 28 days. 

Dalton (1964)

Miss English killed her husband by hitting him with her car. She was charged with murder but got away free because she argued that action were due to severe PMS. Actions should not be held accountable if have PMS. 

Russell Et Al (1980)

Took samples of sweat from a group of women. Rubbed in on upper lip of another woman, foudn their cycles synchronised. Presumably pheromones altered the cycle.

Hersey (1931)

Believed everyone expereinces cyclical mood changes (seasons of the moon). Even if they are unaware of them. 

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AO2: Ultradian Rhythms

Friedman and Fisher (1967)

  • The experiment was conducted in a lab - therefore it can be replicated - and is reliable.
  • The experiment lacks mundane realism - as it was conducted in luxurious isolation - therefore has low ecological validity - and low external validity
  • The experiment couldn't have been effected by demand characteristics - participants acted natural - high internal validity
  • Lacks investigator bias - participants are in isolation

Klien and Armitage (1979)

  • The experiment lacks mundane realism - people do not do 90 minute takss everyday - therefore lacks ecological validity and had low external validity
  • Experiment could be effected by investigator bias as the questions could be different and effected by the investigator
  • Low social desirability bias - measuring the body's cycle. therefore low demand characteristics and so there is high internal validity. 
  • The experiment was conducted in a lab so it can be repeated and there is a high reliability
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AO2: Circadian Rhythms

  • Siffre (1975) 
  • The experiment lacks ecological validity as it was conducted in a cave and therefore cannot be generalised and has low external validity. 
  • It could have been effected by experiementer bias as it was conducted by the experimenter himself (Siffre) therefore this lowers internal validity
  • Results could have been efected by objectivity and therefore it is hard to repeat. 
  • The experiment lacks experimental realism and therefore has low mundane realism
  • Folkard Et Al (1985)
  • The experiment can be replicated and therefore this increases reliability.
  • The experiment was not effected by demand characteristics as the participants didn't know the true aim of the experiment and therefore it has high internal validity
  • However the expeirment lacks mundane realism as there is lowered experiemental realism 
  • Wilkinson (1968)
  • Experiment was not effected by demand characteristics as participants didnt know true aim and therefore there is a higher internal validity. 
  • Not a real life situation and therefore the experiment lacks mundane realism 
  • The results are objective and therefore repeatable meaning they have high internal validity
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AO2: Infradian Rhythms

Dalton (1964)

  • The experiment only focuses on one case study which cannot be repeated therefore it cannot be generalised and has low external validity.

Russell Et Al (1980)

  • Proves that there is a cycle as you can change the cycle, therefore it is reliable as it has scientific evidence.

Hersery (1931)

  • Proves that even bigger cycles can still effect on the mood but is still more gradual.
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Endogenous Pacemakers

The Endogenous Pacemaker is the biological 'clock' in the brain controlling biological rhythms. 

The suprachiasmatic nucleus (SCN) is the pacemaker of the biological clock in all mammals. 

he SCN is a bundle of nerves with a circadian rhythm, this rhythm is created through protien synthesis. The SCN is located in the hypothalamus. 

In Humans and Mammals:

  • Light enters through the eyes and the optical chiasm recieves the input about the amount of light.This light stimulates the SCN which stimulates the pineal gland which is linked to the SCN through a neural pathway. 
  • This produces melatonin (which induces sleep as it enhances serotonin production). When light levels are low high amounts of melotonin are released. 

In birds and reptiles:

  • Light is senses through the thin layer in the cranial bone. This stimulates th pineal gland. The pineal gland has its own pacemaker activity but the incoming light leads to chanes in the amount of melotonin produced. 
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Research into Endogenous Pacemakers


Siffre was underground with no natural light for time cues. He had lots of activities to do but nothign to provide him with any zeitgebers but he still settled in 25 hour rhythm. This shows that it must be internal. 

Aschoff (1965)

Several participants lived together in underground WW2 bunker. All settled into 25 hour rhythm with no external zeitgebers to indicate day or night. 

Binkley (1979)

Showed that glands contain light receptors and the pineal gland secretes the hormone melatonin in inverse proportion to the amount of light falling on the bird: as light decreases melatonin increases. 

Morgan (1995) 

Transplanted SCN cells from mutant hamsters. He removed the SCN from the hamsters and found this this distrupted their circadian rhythm and then it disappeared. Then change

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Evaluation of Research into Endogenous Pacemakers


  • Lacks ecological validity - low external validity as it one case study 
  • Experiment was carried out by experimenter himself and therefore could be effected by experimenter bias 
  • Could have been effected by objectivity and therefore it is hard to repeat


  • Lacks ecological validity as most people dont spend time in an underground bunker
  • Low mundane realism as people again dont spend time in underground bunker
  • High population validity


  • Antrhopomophosis 


  • Anthropomorphosis
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Exogenous Zeitgebers

A 'Zeitgeber' is the german word for 'time giver' and it refers to external stimuli that help in synchronising biological rhythms to the outside world. The most important is light. 

Social Cues

Social cues provide a way of regulating social behaviours and act as the main zeitgeber for circadian rhythms. We eat meals at socially determined times and wake up at times designated for our age. 


Most dominant zietbeger in humans. Daylight has the ability to re-set the biological clock, but dim artificial light is less effective. Aschoff found that if animals are maintained in constant darkness, a brief flash of light will reset their internal clock. Campbell and Murphy (1998) found that shining a light on the back of paticipants knee;s also shifted thier circadian rhythms so therefore it does not just effect the SCN. 

The importance of light as a time-giver can be seen in the difficulties of blind people. Miles Et Al did a case study with a young blind man who's circadian rhythm was 24.9 hours and had to take stimulants in the morning and sedatives at night. 

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Exogenous Zeitgebers Cont.


Further evidence comes from Jerry Linenger, researched by Monk, he lived in a space station for 5 months where the lights malfunctioned and the only indication of light and day he got was from th window which shows 15 day/night cycles every 24 hours. His endogenous pacemaker had become disrupted by the abnormal light cues. 


Biological rhythms can also be entrained by temperature. E.g. Leaves change colour and fall due to changes in temperature. Temp is also a factor in the onset of hibernation. However, there is no research to say that temp afffects human biological rhythms. 

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Disruption of Biological Rhythms

If a biological rhythm is disrupted it can make someones life very uncomfortable and put people at risk. If the zeitgeber changes quickly, problems can occur as the pacemaker cannot keep up. 

Shift Work

Shift work involves regular changes to the hours of work. research indicates that this is bad for people physiologically and psychologically. Working shifts means physiological systems are out of sync with eachother and the envirnoment.

Aschoff (1964)

Introduced the term 'internal desynchronisation'= inbalance of the rhythms. Leads to inpaired performance and potentially dangerous situations. E.g. the accident at the Chernobyl nuclear power plant may have been due to errors made by fatigued night workers. 

Czeisler Et Al staes that frequent shift changes (weekly) are the hardest to adjust to. Longer periods of readjustment (every 3 weeks) are better for workforce and then production. 

Airtraffic controllers usually rotate shifts every few days and they suffer from high rates of hypertension and ulsers, they also have the highest divorce rate of any profession.

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Disruption of Biological Rhythms: Shift Work Cont.

Gordon Et Al states that people on variable shifts are more likely to drink more alcohol, take more tranquillisers and sleeping pills. Artificial lighting is not effective in resetting the circadian rhythm in shift workers. Their body temperatrue also takes a long time to adjust which further affects their performance. Also as the body clock is desynchronised the body can have trouble sleeping, daytime sleeping is typically 1-2 hours shorter than normal REM sleep (Tilley and Wilkinson). As a result they become sleep deprived.


Found that the worst shift patters were which require the workers to adjust their biological clocks backwards (e.g. nights one week and then afternoons, then mornings the next week.) He said the shifts should move forwards instead and each shift should last three weeks.He did a study and found found that by doing this workers reported higher satisfaction, hgiher health and higher productivity. 

Knutsson = People who worked more than 15 hours were 3 times more likely to develop heart disease

Reinberg = People who quit shift work were those who's shifts changed frequently. Happy workers = unchanging rhythms.

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AO2: Shift Work

  • Real life situation = high ecological validity = can be generalised
  • Used a control group
  • Practical value = shows biological rhythms effect.

Ways the effects can be minimised:

  • Longer periods of readjustment (every 3 weeks) CZEISLER are better for the workforce and therefore better for production
  • Shifts should move forwards not backwards CZEISLER
  • Each shift should last 3 weeks
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Disruption of Biological Rhythms: Jet Lag

Jet lag occurs when flying to different time zones (particularily from West to East) It is caused by the sudden discrepancy between the internal clock and the external world. 

One pilot described the effects of jet lag as: headaches, burning or unfocused eyes, stomach upsets, sweating and occasional nightmares. Also for women they can have irregualr periods, insomnia and digestive problems. 

Klien, Wegman and Hunt (1972)

You can recover faster from jet lag after flying from east to west. 

Travellers experience a dysfunction between biological and environmental cues; internal desynchronisation. The symptoms are thought to be caused by melatonin release being out of step with the new envinromental condition. This results in drowsiness at night and insomnia in the day.

Blakemore (1988) - Melatonin supplement pills taken in the evening may reduce the effects of jet lag. Martin (2002) - It can reduce jet lag by inducing sleep.

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Disruption of Biological Rhythms: Jet Lag Cont.

The direction in which you travel can have a major effect on the severity of the jet lag... Most travellers report more diggiculty adjusting when there are flying east. This is because in travelleling east we are attempting to adjust to a shorter day.

Recht Et Al

Analysed major league baseball results in the USA over 3 year period. Teams from New York play teams in Cali which is 3 hours behind New York. Visiting teams which didn't have to cross a time zone between one game and the next won 46% of their games. However when travelling west to east, the percentage of games won fell to 37%. EAST TO WEST ALWAYS BEST.

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AO2: Jet Lag

There are other factors that affect jet lag: you may sleep badly the night before because of worrying. Travel in itself is tiring and may holidays involve long hours of getting to airport. Some people drink alcohol and coffe on the plane which can have harmful effects.

Ways the effects can be minimised:

  • Blakemore - Melatonin pills can be taken in the evening which may reduce the effects
  • Martin - Taking melatonin pills can induce sleep 
  • Melatonin pills can also help your body to adjust to the new time zone
  • You can force yourself to adopt the social rhythms of your new destination. Eat at the right times and go to sleep with local costum from when you get on the plain. 
  • Eating meals at the right time can re-set the biological clock in the liver which might increase enzyme production at the right time for digestion and avoid the stomach upset associated with jet lag. 
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The Nature of Sleep

Sleep is not unconciousness, it is an altered state of consciousness which involves a decreases sense of responsiveness. It occurs daily (circadian) and has distinct stage (ultradian). When we are alseep our depth of our unconciousness vareis throughout the night. Psychlogists can measure our unconcsiousness using an electroencephalograph (EEG). 

There are two types of sleep: NREM and REM 

The Electroencephalograph (EEG) is an apparatus that records electrical activity in the brain. Electrodes are taped to the head of the participant and the machine produces a readout as a long on a roll of paper or a screen. When the peaks and troughs on the line are close togehter it is in high frequence or fast. When the peaks and troughs are more spaced out, it is low frequency or slow. 

NREM is called slow-wave sleep and only refers to the last two stages of sleep, with slow delta waves. 

REM is when a person dreams and has brain activity like they are awake. The EEG will show an aroused pattern but the body is paralysed. 

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Nature of Sleep Cont..

Brain waves are divided into four bands: beta, alpha, theta and delta:

  • Beta - Normal working thought, alter problem solving
  • Aplha - Deep relaxation, meditation or a 'blank' mind
  • Theta - Light sleep
  • Delta - Deep, dreamless sleep 

Sleep is not a continous resting state. Whne a persons EEG is taken whilst sleeping there are distinctive changes at regular intervals. 

When the EEG becomes desynchronised and theta waves start to appear this is the sign the person is properly asleep and has entered stage 1. The EEG changes again as the person enters stage 2. The trace now shows slightly higher voltage waves and the spindles and K-complexes appear for the first time. Eventually the person moves on to stage 3. Slow, hgih voltage delta waves beign to appear. After a short period the person enters stage 4 where the EEG shows almost all delta waves. 

At various points in the night, the person will enter REM sleep. Here the EEG shows a trace like that of a person who is awake. REM stands for Rapid Eye Movements. 

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Stages of the Sleep Cycle

Stage 1:

Relaxed state, brain waves change from beta waves (awake) to alpha waves which are slower, more regular and have greater amplitude. Alpha waves start to become theta waves. Heart rate slows and muscles relax.

Stage 2:

Slower, larger brain waves, short bursts of high frequency sleep spindles and K-complexes. This is light sleep and the sleeper is easily woken.

Stage 3:

More slwoing down of brain waves and bodily acitivty (e.g. heart rate). Long, slow delta waves with some sleep spindles. This is deep sleep and the sleeper is not eaisly woken.

Stage 4:

Slow wave sleep (SWS) with more delta waves than stage 3. Hard to be woken, some physiological acitivitys take place e.g. production of growth hormone. Also, sleep walking, talking and night terrors. Heart rate, blood pressure and body temp are as low as can get. 

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'The Sleep Escalator'

Most people have 5 cycles of sleep a night that last approximately 90 minutes. Slow-wave sleep (SWS) occurs only in the first two cycles. REM occurs in all of the cycles and increases during the course of the nights sleep. 

EEG's = measure electrical activity or brain waves

EOG's (Electro-oculograms) = measure eye movement 

EMG's (Eletromyograms) = measure muscle movement and have been used to distingush the stages and cycles of sleep. 

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Research into the Nature of Sleep

Pieron, Klietman and Aserinsky

In 1913 Henri Pieron authored a book which was the first text to examine sleep from a physiological perspective. Dr. Nathaniel Klietman, now known as the ''Father of American sleep research'' began work in the 1920's questioning the regulation of sleep and wakefulness of circadian rhythms. In 1953 one of his students Aserinsky, made the landmark discovery of REM during sleep.


During the 1930's Berger developed the EEG. This detected electrical activity within the brain. He tested it on participants and found that when they slept their brain waves changed periodically during the sleep period. 

Dement and Jouvet 

One of Kleitman's students Dement, extended Kleitmans path of research. Dement described the ''cyclical'' nature of sleep and showed a relationship between REM and dreaming. Dement and Kleiman tested on patients and found correlation betweent two. 

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AO2: Nature of Sleep

  • There are problems with the scientific study of sleep: A lot of research has been conducted using animals in captivity. More recent research of these animals in their natural habitat have illustrated that these studies are unreliable due to the conditions they were conducted. The findings in captivity may have been due to boredom or the monotony of life.
  • The research methods have advanced and now give a more comprehensive picture: With the advancement of the polysomnography we now have a broader picture of the nature of sleep.
  • The study of sleep is scientific; The methods used are objective as they are measuring bodily responses which need little subjective judgemet. Therefore the research is open to being falsified. Sleep patterns in the lab (a very artificial envinroment) may not represent th esleep patterns in a persons home. 
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Lifespan Changes in Sleep


Babies sleep a lot more than adults. The amount that we sleep diminishes as we get older. Babies sleep an average of around 16 hours per day, almost half of this is REM sleep.

This is examplined by the considerable amount of learning and brain development happening in the first few months of life. Premature babies spend 90% f their time in active sleep (growign ect.) New borns have both quiet and active sleep.


When an infant reaches 5 years old thieir brain acitivtity looks like an adults on an EEG. The frequency of th ewaves is different to adult sleep patterns. For example, there is still more REM sleep (about 30% total sleep time) and less stage one sleep.

Boys sleep slightly less than girls during childhood and more sleep disorders will form during childhood. 

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Lifespan Changes in Sleep


Adolesents will often sleep for around 9 hours a day, during the teenage years the need for sleep increases and they can often sleep for a lot longer. 

A large feature of teenage REM sleep is tending to ****** or ***********. During these years teenagers circadian rhythms can also adjust and they are more awake at night and have more difficulty waking up.

Adulthood/Old Age:

REM sleep declines to around 20-25% of total sleep time and there is a large increase in stage two sleep (up to around 60%)

The amount of SWS declines as well, ebing redcued to as little as 5% and in some very old people this ay be non-existent. 

Kripe Et Al (2002) surveyed over one million men and women and found that people sleeping for only six or seven hour had a reduced mortality rate. 

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