Circadian Rhythm - a cycle that occurs once every 24 hours.
E.G Sleep- wake cycle
Infradian Rhythm - a cycle that occurs less than once every 24 hours.
E.G Menstrual cycle
Ultradian Rhythm - a cycle that occurs more than once every 24 hours.
E.G the stages of sleep.
Sabbagh and Barnard (1984) found that women who live together may have a synchronised menstrual cycle.
EEG scans show that a regular sleep pattern is really important. And disrupting it may lead to serious consequences.
Internal & External Influences
Endogenous pacemakers (Internal)
1.The SCN, part of the hypothalamus, acts as an internal clock to keep the body on an approximate 24 hour sleep - wake cycle.
2. The SCN regulates the pineal gland which secretes melatonin- a hormone that induces sleep. When there is less light, more melatonin is produced, when there is more light, secretion is reduced and waking occurs.
Evidence for: Menaker et al (1978) experimented on hamsters and removed the SCN this caused a disruption in their sleep wake cycle. When SCN was replaced sleep wake cycle returned to normalcy.
Exogenous Zeitgebers (External)
1. These are influence that act outside of the body like a prompt, triggering a biological rhythm.
2. Light is the most important zeitgeber. Siffre (1975) spent six months in a cave. He had no clocks and no natural light. His sleep - wake cycle extended to 25 - 30 hours. It seems natural light is needed to fine tune our normal 24 hour cycle.
Interaction between Internal & External Factors
Endogenous and Exogenous factors interact to regulate the timing of biological rhythms.
In some cases endogenous factors may completly determine a cycle. Pengelly & Fisher (1957) found that squirells still hibernate even when kept in lab conditions.
However, many animals can react more flexibly, especially humans who are able to adapt their surroundings. We are able to force ourselves to stay awake amd change the environment to suit our needs.
Cultural factors are also important, for example eskimos live in permanent daylight and permanent night but are able to maintain regular sleep wake cycles. So the cycle can't just be determined by levels of light acting on the pineal gland.
Individual Differences can affect biological rhythms Aschoff and Weaver (1976) found that in a group of people isolated from daylight, some maintained regular sleep wake cycles while other members displayed their own extreme idiosyncrasies, E.G 29 hours awake followed by 21 hours asleep. This also shows that factors must interact to control or influence biological rhythms.
Disrupting Biological Rhythms
In the natural environment zeitgebers change slowly, however in modern society zeitgebers can change quickly this can have negative effects on our ability to function
Travelling East to West (Phase Delay) makes you sleepier at an earlier local time. Best way to adapt to this is by forcing yourself to stay awake. Travelling West to East (Phase Advance) is harder to adapt to and can take up to a week to fully synchronise.
Wegmen et al (1986) found that the statements above were true.Schwartz et al (1995) found that American baseball teams from the east coast got better results travelling to play in the west than west coast teams travelling to play in the east.
Czeisler et al (1982) studied workers at a factory whose shift patterns appeared to cause sleep and health problems. The researchers reccomended 21- day shifts allowing more time for workers to adapt, and changes shifts forward in time (phase delay) after these changes productivity increased as did job satisfaction.
Points to consider in Research into Biological Rhy
1) Research on animals can't be generalised to humans. Also done under lab conditions which are considerably different to animals natural habitats, but as a high degree in controlling variables
2) Research into light deprivation allowed artificial light which may give benefits of natural light thus lowering its validity.
3) Things like Individual differences need further study,as some people are more alert early in the day and others later on in the day. Also the speed in which we adapt to disruptions can vary. Its difficult to establish whether a persons lifestyle is a cause or effect of their biological rhythm.
4) Although studies into zeitgebers has established their existence, the importance of each is still unclea as it the nature of their interaction.
5) Number of participants especially in Siffre's cave study lowers the validity of the research as it may be due to that persons individual differences
Points To Consider in Research of Disrupting Biolo
1) Consistent Evidence shows that disrupting biological rhythms can have cognitive and emotional effects on people.
2) Much of the research is generated through the use of field studies that have a high ecological validity, but many confounding variables, such as personality types and other individual differences are not controlled. This makes it difficult to reach firm conclusions about the causal influences in any resulting behavaiour.
3) Although there are examples where disrupting biological rhythms has drastic effects, many thousands of people carry out shift work without any obvious effects on their cognitive abilities, such as concentration and attention. This demonstrates an ability of our biological rhythms to adapt to changing environmental circumstances.
The 5 Sleep Stages
There are 5 stages of sleep, Adults pass through the stages about 5 times a night, with each cycle lasting about 90 minutes.
As you fall deeper into sleep brain activity becomes a higher voltage but lower frequency.
Stage 1: Easy to wake people up, lowered heart rate,muscle tension and temperature.
Stage 2: Slower and larger EEG waves with some quick bursts of high frequency waves called sleep spindles.
Stage 3: Even larger slower waves.
Stage 4: deepest stage of sleep, metabolic activty is low and sleeper is hard to wake.
After stage 4 the cycle reverses back through stages 3 and 2 a period of active sleep occurs instead of stage 1.
During the active stage, metabolic activity increases, and the body appears almost paralysed except for rapid eye movement (REM). EEG pattern almost like when awake. Cycle repeated 5 times but only enter stages 3 & 4 in the first 2 cycles. Periods of REM increase with each cycle.
Theories of Sleep; Evolutionary
Webb (1968) suggested that sleep is like hibernation and conserves energy at times when it is harder to get resources when using energy would be inefficient.
Meddis (1977) suggested that sleep helps keep animals safe by being quiet and still. They are therefore less likely to attract predators at night, however it also makes animals vulnerable to predators if discovered.
Sleeping occurs in all animals so it must be an important function. Although sleep varies from animal to animal as the predators sleep alot in contrast to their prey which sleeps very little.
This approach is useful to understand how and why behaviours occur. However evolution has occured over along time so it is hard to test theories about why some behaviours have been naturally selected. So it is difficult to falsify making it less useful from a scientifice perspective.
Theories of Sleep; Restoration
Oswald (1980) suggested that SWS is for restoring bodily functions linked to physical activity and REM sleep is for restoring brain functions.
Horne (1988) distinguished between the 2 types of sleep, core sleep which is made up of the 4 stages of SWS for body restoration and optional sleep which is made up of other sleep stages, Optional is not necessary, however having it can conserve energy.
It seems that important brain and body restoration occurs during sleep. Babies, whose brains are developing spend more time in REM sleep and release more growth hormone during SWS.
Sharipo et al (1981) found that long distance runners had more SWS after a race, implying that exercise increased the need for body restoration.
However Horne and Minard's (1985) study found that when participants did physical and cognitive activity fell asleep quicker but not longer. It may be that there was a reduction in the amount of optional sleep they had.
Lifespan Changes in Sleep
The amount we sleep and our patterns of sleep change as we get older.
The older we get the less we tend to sleep, babies sleep up to 20 hours a day, whilst most adults average 7-8 hours and people over 50 only 6 hours.
Also as we get older we tend to have less REM sleep - Kleitman (1963) found that newborns spend 8-9 hours every day in REM sleep. Children have less REM sleep than infants, and adults have less than children.
Kales and Kales (1974) found that elderly people are more likely to wake up several times during their nights sleep than younger people.
Evidence for Lifespan Changes in Sleep
Most evidence for changes in sleep patterns comes from laboratory research using EEG recordings. These recordings are obtained by attaching electrodes to participants. This creates an unfamiliar sleeping environment for the participants, which may disrupt their usual sleep patterns.
However Empson (1989) suggests that after the first night participants adjust to their conditions and their sleep is representative of their usual patterns.
More research is needed to find out the reasons for lifespan changes in sleep. For example, REM sleep in childhood may be linked to brain development.
Techniques used in Sleep Research
EEGs meaure electrical activity and provide quantative reports which can be easily compared to others. The have high reliability and changes in sleep stages can be easily identified.
Other equipment used includes EOGs which measure the electrical activity of the eyes and EMGs which measure electrical activity in muscles.
Self reports involve participants keeping a record of their dreams or estimating their length. They're useful for gaining information which couldn't be collected in any other way, but they're limited by the accuracy of recall.
Observations of patterns and directions of eye movements can be recorded and related to sleep stages.
Variables such as noise are controlled to increase reliability of the research. However, research in sleep laboratories creates an artificial environment, which may affect the participants sleep patterns and reduce validity.
Sleep Disorders; Insomnia
People with insomia have difficulty staying asleep, falling asleep or both.
The may feel sleepy and irritable during the day with impaired concentration, this can effect their daily lifes and relationships.
Insomnia may be acute lasting a few nights or chronic, lasting weeks, months or years.
Research suggests that 10% of adults may suffer from chronic insomnia.
There are 2 types of insomnia.
Primary & Secondary.
Sleep Disorders; Primary Insomia
Primary insomnia is insomnia that is not linked to any existing physical or psychological conditions, Instead it may be caused by;
1. Stimulants, such as caffeine or nicotine increase arousal and can lead to insomnia. This can lead to a viscious circle of frustration and anxiety.
2. Disruptions of circadian rhythm. Jet-lag, shift work and sleeping at irregular times may all disrupt sleep patterns and lead to insomnia.
Sleep Disorders; Secondary Insomnia
Seconday insomnia is the result of existing physical and psychological conditions. It may be caused by;
1. Physical complaints. a number of physical complaints such as arthritis, diabetes and asthma can cause insomnia.
2. Psychological conditions. for example depression can cause insomnia.
3.Stress or Anxiety. Worry about something causes anxiety, which increases body arousal which can in turn cause insomnia. Failure to sleep can cause frustation, which creates more anxiety making it even harder to sleep.
4. Medication. Some medications may have side effects which disrupt sleep. Some people may become dependant on sleeping pills and suffer even worse insomnia if they stop taking them.
Factors affecting Insomnia
An episode of insomnia can be influenced by many factors such as;
1. Sleep Apnoea. This condition is where a persons airways become temporarily blocked whilst they are sleeping, causing their breathing to be interrupted. This disrupts their sleep pattern by either causing the person to wake up or move into a lighter stage of sleep. Sleep apnoea is linked to snoring and may be caused by various abnormalities in brain or respiratory functioning. It is also linked to obesity.
2. Personality Traits. Characteristics like being overly sensitive, worrying, having a very serious attitude to life issues and being overly dependant on other people can lead to insomnia.
3.Depression and Anxiety. These increase emotional arousal which may then increase physiological arousal causing insomnia.
Research into insomnia is difficult as there are many variables that can cause or influence the condition. Some variables are hard to control. Much of the research thats been done produced a positive correlation rather than a cause and effect.
Sleepwalking is a disorder associated with stage 3 & 4 sleep. It affects approximately 15% of children and 2% of adults. The causes of sleepwalking are not fully known but its thought it can be triggered by...
Sleep deprivation especially in people with a history of sleep walking.
An irregular sleep schedule.
Stress or anxiety
Some drugs such as anti psychotics and stimulants.
Dauviliers et al (2005) study suggests there may be a genetic component to sleepwalking aswell, they found higher concordance rates for the disorder in identical twins than in non identical twins.
Narcolepsy is a disorder which causes sudden episodes of daytime sleepiness, leading to the person falling asleep during the day for a short period of time. They may also experience features of sleep such as weak muscles (cataplexy) and dream like imagery. Narcolepsy effects 0.02-0.06% of the population, most of whom develop the condition in early adulthood. The causes of this disorder may include;
Reduced levels of hypocretin. This chemical is involved in regulating arousal levels. Its thought narcolepsy may be caused by the bodys immune system attacking the cells that produce hypocretin, reducing the bodys ability to regulate sleep.
Genetics. Studies have shown that a 25-31% concordance rate for the condition between identical twins. The concordance rate is faily low however so environmental influences must be important.