Biological Rhythms

• Biological Rhythms


  distinct patterns of changes in body activity that conform to cyclical periods.
• Circadian rhythms 


  biological rhythms with a 24-hour cycle e.g. body temperature or the sleep-wake cycle
• The sleep-wake cycle


  The sleep-wake cycle is influenced by exogenous zeitgebers like light and endogenous zeitgebers, our biological 'clock' called the supercharacteristic nucleus (SCN) located just above the optic chiasm which provides information from the eye about light. Exogeneous zeitgebers can reset the SCN.
• Siffre's Cave study


  Siffre spent several extended periods of time in caves without exposure to natural light or sound to study the effect of his biological clock. in 1962 he spent 2 months in a cave in the southern Alps. A decade later he did the same for 6 months in a Texan Cave. In each case his 'free running' biological rhythm settled to a cycle of about 25 hours and he continued to wake and sleep in a regular schedule.
• Bunker study


  Similar results to Siffres were found in Aschoff and Wever (1976) study where a group of participants spent 4 weeks in a World War 2 bunker deprived of natural light. All but all but 1 participants displayed a circadian rhythm of 24 to 25 hours. Both Siffre's experience and the bunker study suggested the same natural sleep-wake cycle may be slightly longer than the 24-hour but that is entrained by exogenous zeitgebers associated with our 24-hour days.
• Folkard et al.s cave study


  Folkard et al (1985) studied 12 people who agreed to live in a cave without natural light for 3 weeks, going to sleep at 11:45 and waking at 7:45. Over the course of the study, researchers gradually sped up the clock so a '24 hour day' was only actually 22hrs. Only one participant was able to comfortably adjust to this. Suggesting the biological clock cannot be easily overridden by exogenous zeitgebers.
• Shift work and Circadian rhythms


  One strength of research into circadian rhythms is it provides an understanding of the consequences of them being disrupted. For example, night workers experience a period of reduced concentrations around 6 am meaning mistakes and accidents are more likely. Research has also linked shift work and poor health, being three times more likely to develop heart disease. This shows research may have real-world economic implications in terms of managing worker productivity.
• Counterpoint to research into shift work and circadian rhythms

  However, studies investigating the effects of shift work tend to use correlational methods. Meaning it is difficult to establish whether disruption to the sleep/ wake cycle is actually the cause. Solomon (1993) concluded high divorce rates in shift workers might be due to the strain of deprived sleep and other influences such as missing out on family events. This suggests it may not be biological factors that create the consequences associated with shift work.
• Strength of research into circadian rhythms for treatments

  Research into circadian rhythms has been used to improve medical treatments. Circadian rhythms govern basic processes like heart rate, digestion and hormone levels. These rise and fall during the day, leading to the study of how medical treatment can be administered according to a person's biological rhythms. Aspirin for heart attacks is the most effective last thing at night as heart attacks are more common in the morning so timing matters. Showing how research can help increase the effectiveness of drug treatment.
• Limitation of research into circadian rhythms


  A limitation of research is generalisations are difficult to make. Studies into CR often have very small samples and it seems that sleep/ wake cycles vary from person to person. Czeisler found individual cycles varied from 13 to 65 hours. Duffy et al found some people have a natural preference for sleeping early and getting up early or the opposite. Even Siffre observed his sleep/ wake cycle slowed over time. Meaning it is difficult to use research data to discuss more than averages, which may be meaningless.
• Circadian rhythms and the school day

  Researchers have suggested the school day should start a couple hours later to fit with the typical teenage sleep/wake cycle. Hormonal shifts in the teenage body mean getting to sleep can be more difficult and they are more tired at the start of the school day. Research has shown benefits for academic and behavioural performance when lessons start later and a reduction of caffeine dependence. However this is destructive to teachers and parents and limits after-school activities.
• Infradian rhythms


  biological rhythms that happen less than one in 24 hrs e.g. menstruation or seasonal affective disorder.
• Exogenous factors on the menstrual cycle


  There is evidence to suggest there are exogenous zeitgebers such as other women's menstrual cycles that affect a person's cycle. Stern and McClintock et al. (1998) studied 29 women with a history of irregular periods and exposed them to the pheromones of nine women at different stages of their cycle. On day one they were exposed to pheromones of day one in the cycle, day two exposed to day two etc. 68% of women experienced changes to their cycle, brining them closer to the cycle of the 'pheromone donor'
• Seasonal affective disorder


  SAD is a type of depressive disorder characterised by low mood triggered during the winter months. It is a circannual rhythm as it is yearly, however, it can also be classed as a circadian rhythm as it may be due to the disruption of the sleep/ wake cycle due to earlier periods of darkness and shorter daylight hours.
• Role of melatonin in SAD


  Psychologists suggest melatonin is involved in the cause of SAD. During the night the pineal gland secrets melatonin till dawn when there is an increase in light. The lack of light in the morning means secretion continues for longer. This is thought to have a knock-on effect on the production of serotonin- a chemical linked to the onset of depressive symptoms.
• Ultradian rhythms


  biological rhythms that occur more than once in 24 hrs e.g. the stages of sleep (sleep cycle)
• Stages of sleep


  The most researched ultradian rhythm is the sleep cycle. It consists of 5 stages and lasts abut 90 minutes, repeating thought the night. Each stage is characterized by different types of brainwaves which can be monitored by EEGs.
• Stages 1 and 2 of sleep

  Light sleep, a person may be easily woken. Brain Alpha waves are high-frequency and short-amplitude. In stage 2 the alpha waves continue but there is occasional random changes in pattern called sleep spindles.
• Stages 3 and 4 of sleep

  Deep Sleep or slow-wave sleep (SWS). The brain waves are delta waves with lower frequency and higher amplitude. It is difficult to wake someone from this.
• Stage 5 sleep (REM)


  The body is paralysed but brain activity closely resembles an awake brain. Theta waves are produced and the eyes occasionally move around, aka Rapid Eye Movement. Dreams are most often experienced during REM sleep, but may occur in deep sleep.
• Strength of menstrual synchrony research

  A strength of menstrual synchrony research is it may be explained by natural selection. For our distant ancestors, it may have been advantageous for females to menstruate together and become pregnant at the same time. In a social group, this would allow babies who had lost their mother during or after childbirth to have access to breast milk, thereby improving their chances of survival. This suggests synchronisation may be an adaptive strategy.
• Limitations of menstrual synchronisation research

  A limitation of synchronisation studies is their methodology. There are many factors that affect change in a woman's cycle, including stress, changes in diet, exercise etc. These may be confounding variables and any findings may be by change. this may explain why other studies have failed to replicate findings. This suggests menstrual synchrony studies are flawed.
• Real-world applications for understanding factors affecting SAD


  One of the most effective treatments for SAD is light therapy, a box that stimulates very strong light to reset the body's internal clock, reducing the effects of SAD in about 80% of people. This is preferred over antidepressants as it is regarded as safe. However, light therapy can cause eye strain and headaches. Rohan et al recorded a relapse rate of 46% over successive winters, compared to 27% receiving CBT.
• Strength of research into ultradian rhythms

  A strength of research into ultradian rhythms is it has improved understanding of age-related changes in sleep. Scientists have found deep sleep reduced with age. According to Cauter et al, this may explain various impairments that come with old age, such as reduced alertness. In order to increase SWS, relaxation and medication may be used. Suggesting knowledge of ultradian rhythms has practical value.
• Limitation of research into ultradian rhythms


  One limitation of research into ultradian rhythms is there is significant variation between people. Tucker et al found large differences between people in terms of duration of each sleep stage, particularly stages 3 and 4. Tucker et al suggested that these differences are likely biologically determined. This makes it difficult to describe normal sleep.
• Strength of sleep research methodology


  One of the benefits of sleep research is it is done in a sleep lab where there is control over extraneous variables like noise. However, lab studies involve being attached to complicated machinery, and may not represent a participant's's ordinary sleep in any meaningful way.
• The suprachiasmatic nucleus

  The SCN is located in the hypothalamus in each hemisphere of the brain. It is one of the primary endogenous pacemakers in mammals and is influential in maintaining circadian rhythms. Nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the left and right visual centres. The SCN is just above this and receives information about light from it. even when asleep our biological clock adjusts to changing patterns while we are sleeping.
• Animal studies on the SCN

  DeCoursey et al. (2000) destroyed the SCN of 30 Chipmunks who were returned to their natural habitat. and observed for 80 days. Their sleep/ wake cycle disappeared and a significant amount were killed by predators, presumably because they were awake and active, vulnerable to attack when they should've been asleep.

  Ralph et al. bred 'mutant' hamsters with a 20-hour cycle. When SCN cells from the foetal tissue of a mutant hampster were transplanted into normal hampsters, the cycles defaulted to 20 hours.
• The pineal gland and melatonin in the sleep/ wake cycle


  The SCN passes the information on day length and light to the pineal gland (just behind the hypothalamus) During the night the pineal gland induces the production of melatonin which induces sleep and is inhibited during waking hours. Melatonin has also been suggested as a casual factor in SAD.
• Entrainment 


  The adjustment of a behaviour to synchronize or be in rhythm with another behviour
• Lights role in the sleep/ wake cycle

  Light can reset the body's main endogenous pacemaker the SCN and therefore plays a role in the maintenance of the sleep/ wake cycle. It also has an indirect influence on key processes in the body such as hormone secretion and blood circulation.
• Researcher into light effect on the sleep/ wake cycle


  Campbell and Murphy demonstrated that light may be detected by the skin receptor sites even when not received by the eyes. Fifteen participants were woken at various times and a light pad was shone on the back of their knees. The researchers managed to produce a deviation in the participant's usual sleep/ wake cycle of up to three hours in some cases. This suggests that light is a powerful exogenous zeitgeber that doesn't necessarily rely on the eyes to have an influence on the brain.
• Social cues involvement in the sleep/ wake cycle

  Babies are not on the same sleep/ wake cycle as everyone else and is pretty much random. By 6 weeks the circadian rhythms begin and by about 16 weeks babies' rhythms have been entrained by the schedules of parents, including parent-determined meal times and bedtimes.

  Research on jet lag suggests that adapting to a local time for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances.
• Limitation of SCN research


  A limitation of SCN research is that it may obscure other body clocks. Research revealed there are numerous circadian rhythms in many organs and cells in the body. These are found in organs including the lungs, pancreas and skin. They are influenced by the actions of the SCN but also act independently. Damiola et al demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours whilst leaving the rhythm of the SCN unaffected. This suggests other complex influences on the sleep/ wake cycle.
• Limitation of studying endogenous pacemakers


  A limitation of studying endogenous pacemakers is they cannot be studied in isolation. Total isolation studies such as Siffre's cave study are extremely rare. He also used an artificial light which could have reset his biological clock every time he turned it on. In everyday life, pacemakers and zeitgebers interact and it may make a little sense to separate the two for the purpose of research. This suggests the more researchers attempt to isolate the influence of internal pacemakers. the lower the validity of the research.
• Issues with animal studies on the sleep/ wake cycle

  Animal studies are justified because there are very similar mechanisms at work across species. The existence of a SCN and pineal gland in the brain means that generalisations can be made to the human brain, as the human brain has similar mechanisms. However, there are serious ethical issues. For example, animals in DeCoursey et al's study were exposed to risk when returned to their natural habitat and most died as a result.
• Limitation of research into exogenous zeitgebers


  A limitation is that exogenous zeitgebers do not have the same effect in all environments. The experience of people who live in places where there is very little light in the summer for example, Inuits of the Arctic Circle, are said to have similar sleep patterns all year round, despite spending around six months in almost total darkness. This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental charges in light.
• Case study evidence for exogenous zeitgebers


  Another limitation is evidence challenges the role of exogenous zeitgebers. Miles et al. recount the study of a young man, blind from birth who had an abnormal circadian rhythm of 24.9 hours. Despite the exposure to social cues such as regular meal times, his sleep-wake cycle could not be adjusted. This suggests social cues alone are not effective in resetting the biological rhythm.
• Age-related insomnia


  Evidence suggests people have poorer quality of sleep as they get older. This may be due to natural changes in the circadian rhythm as we age, which means falling asleep earlier and broken up sleep at night. However, studies have suggested exogenous factors may be more responsible for the changes in sleep patterns among older people. Hood et al found management of insomnia was improved if elderly people were generally more active and had more exposure to light.