- Created by: Ikra Amin
- Created on: 11-01-15 21:37
Circadian - A rhythm that happens once every 24 hours (sleep-wake cycle for example)
Infradian - A rhythm that happenes once a month or year, it's infrequent (menstrual cycle)
Ultradian - A rhythm that happens more than once in 24 hours and is less than 24 hours, ultra (hunger)
Endogenous pacemakers - Internal cues that have an influence on rhythms
Exogenous zeitgebers - External cues that have an influence on rhythms
The term biological rhythm refers to cyclical behaviours, ie behaviours that are repeated periodically. These are controlled either by endogenous pacemakers (internal biological clocks regulating biological functions) or by exogenous zeitgebers (external/environmental cues, like seasonal change, clocks etc)
- Stayed in a cave for 6 months and was isolated
- Removed all exogenous zeitgebers (natural light, clocks)
- Found that for the 1st month he had regular sleep-wake cycles (slightly longer than 24 hours)
- When he emerged they found that his mind had lost track of time but his body didn't. He unintentionally kept regular cycles of sleeping and waking
- Average day for him lasted a little over 24 hours, discovered humans have internal clocks
- Endogenous pacemakers stronger in this study than the exogenous zeitgebers because the circadian rhythm did not change that much
These are biological cycles lasting around 24 hours. The two best known circadian rhythms are the sleep/wake cycle which is usually facilltated by time checkd and regular events like heart rate, body temp cycle, rising and falling as an indicator of metabolic rate.
RESEARCH INTO CIRCADIAN RHYTHMS
The sleep-wake cycle
Siffre's work has shown how important endogenous pacemakers are to our biological rhythms and our everyday functioning.
Aschoff and Wever (1976)
- placed p's in undeground WW2 bunker with no environmental and social cues (no clock, time cues etc)
- they found that most people displayed circadian rhythms between 24 and 25 hours, though some rhythms were as long as 29 hours
- this suggests that endogenous pacemakers control the sleep-wake cycle in the absence of light cues, though external cues are important to some extent since, left to their own devices, the internal clock was not perfectly accurate. It varied from day to day.
- endogenous pacemakers stronger (that kept sleep wake cycle) but the exogenous zeitgebers important too. Exogenous zeitgebers entrain the endogenous pacemaker.
Folkard et al (1985)
- isolated 12 p's from natural light for 3 weeks, manipulating the clock so that only 22 hours passed a day
- asked p's to go to bed at 11:45pm and get up at 7:45am
- at first the clock ran normally, but then they quickened the pace so that when the clock said 24 hours had passed only 22 had actually passed
- at first p's circadian cycle matched the clock, but, as it quickened, their rhythm no longer matched the clock and continued to follow a 24 hour cycle rather than the 22 hour cycle imposed by the experiment.
- overall, this suggests that the circadian rhythm can only be guided to a limited extent by external cues.
- Endogenous pacemakers stronger than exogenous zeitgebers
However, once p's are back in their everyday life they take only a few days to resynchronise their cycles to the available external time cues (e.g. light and noise), meal times etc.
Core body temperature
Core body temp changes throughout the day. It is lowest at about 4:30am (36deg) and highest around 6pm (38deg). There is a slight dip after lunch (not just due to eating) and the practice of having a nap is related to this.
Hormone production follows a circadian rhythm. Cortisol (stress hormone) is at its lowest around midnight and peaks around 6am. Melatonin (which induces sleepiness) and growth hormone are two other hormones that have a clear circadian rhythm, both peaking at around midnight.
Commentary/evaluation on research into circadian r
Research methods: In almost all early studies into the sleep-wake cycle p's were isolated from variables that might affect their circadian rhythms, such as clocks, radios and daylight. However, they were not isolated from artificial light. Research, E.g. Czeisler et al (1999), has actually made use of artificial light to deliberately alter p's circadian rhythms, manging to change rhythms down to 22 hours and up to 28 hours. <- this all reduces validity findings. Most isolation studies have few p's, making generalisation a problem. This means the population validity of the findings is low.
Individual differences: Duffy et al (2000) found that early risers prefer to get up early and go to bed early (6am-10pm),whereas evening people prefer to wake and go to bed later (10am-1am).
Aschoff and Wever (1976) found in isolation studies that some p's maintain normal cycles, while others strongly differ. Again, the validity of findings is reduced since it is difficult to determine whether findings are the result of universal sleep-wake cycles, or simply the result of everyone being different.
Real world application: Chrono therapeutics is the study of how timing affects drug treatments. Since the circadian rhythm affects digestion, heart rate, hormone secretions and other functions, this should be taken into account when taking drugs. E.g. 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.
Folkard et al (1977) looked at the learning ability of 12 and 13 yr old children who had stories read to them at either 9am or 3pm. After 1 week, the afternoon group (higher core body temp) showed both superior recall and comprehension, retaining about 8% more meaningful material. This suggests that long term recall is best where body temp is highest. This has implications for students taking exams.
IDA: Low pop validity and low generalisability
These are biological cycles lasting more than 24 hours, e.g. the mestrual cycle, which is regulated by hormone secretions.
- Function of the mestrual cycle: Regulate ovulation.
- Role of pituitary gland in this cycle: releases hormones to stimulate the ovary to produce estrogen and progesterone.
- Principle hormones in menstrual cycle & what they do: Estrogen, involved in thickening of the inner lining of the uterus in readiness for pregnancy & progestrone causes the lining of the womb to prepare for a pregnancy by increasing its blood supply. About 2 weeks after ovulation, if there is no pregnancy, progestrone is reduced and this causes the lining of the womb to be shed. (Levels of both of these change during the cycle).
Menstrual synchrony studies
- Although the menstrual cycle was identified years ago, how it is generated and how it interacts with other factors is not fully understood.
- It is affected by circadian rhythms, as the secretion of luteinising hormone, which starts ovulation and is produced by the pituitary gland which has been stimulated by the hypothalamus, occurs in the early morning hours.
- Phase shifts occurring due to jet lag can also affect mestrual cycles.
- The menstrual cycle is affected by both endogenous and exogenous cues. The investigation of one of the external factors has focused on the role of pheromones in determining when ovulation occurs.
- Pheromones are chemical substances released by various different animal species that can affect the behaviour of other members of the species.
- It's been suggested that human females emit pheromones that can influence the menstrual cycles of women around them.
Research into pheromones
McClintock and Stern (1971 and 1988)
Aim: To investigate the role of pheromones in the synchronisation of the menstrual cycle amongst women living in close proximity.
- Involved a 10 yr longitudinal study involving 29 women aged 20-35 yearsm with a history of irregular, spontaneous ovulation.
- The researchers gathered samples of pheromones from 9 women at certain points in their menstrual cycles by placing pads of cotton under their arms.
- The women had previously bathed without perfumed products and wore the cotton pads for at least 8 hours.
- Each cotton pad was treated with alcohol to disguise odours and was frozen.
- These pads were wiped under the noses of the 20 other women on a daily basis.
- 68% of women responded to the pheromes.
- Menstrual cycles either shortened from 1 to 14 days, or lengthened from 1 to 12 days, depending on when pheromones were collected.
- Pheromones from women in the early phases of their cycles shortened the cycles of the 2nd group of women (between 1 and 14 days) by speeding up their pre-ovulatory surge of luteinising hormone.
- Conversely, pheromones collected later, during ovulation, lengthened the menstrual cycles (by 1-12 days) by delaying the luteinising hormone surge.
Conclusions: It is unclear how pheromones trigger menstrual cycle changes. Because the samples were put on p's top lips, McClintock admits to not fully understanding whether the chemical is acting through the skin, the mucus membranes in the nose, or a pair of tiny pits in the nose.
- The results found by McClintock concerning synchronisation of menstrual periods can be explained as random occurrences and do not form a significant difference statistically. Also, women's cycles are not universal, which may invalidate findings. What is needed is evidence that women with different cycle lengths shown synchronisation.
- It may well be that there was once an evolutionary advantage to having all the women in a community menstruate at the same time, however, there is no strong evidence that this is the case.
- Human production of, and response to, hormones is questionable. Researchers have not yet discovered the precise substance involved or the mechanism by which it affects the menstrual cycle.
- A study examining a women's basketball team for an extended period found no correlation between menstrual patterns. However, exercise, dieting and stress can cause changes in womens menstrual patterns and these may have affected synchronisation.
- Their research has further support, E.g. Russell et al's (1980) work citing pheromones as an exogenous zeitgeber.
- The evidence for pheromones have been extracted and analysed. However, generalising from animals to humans is controversial, as animal behaviour is not always reflective of human behaviour.
Evaluation cont (eval points linked to core statements on previous card):
- Further research has produced similar findings,, suggest concurrent validity is high. (bullet point 5)
- Alternative research findings have contradicted the findings, questioning the validity of research (4)
- Findings based on animal research have supported the validity of findings (6)
- The validity of the findings may be threatened by individual differences in the way women's bodies work, which have not been controlled in this research.
Exogenous zeitgebers in this study; pheromones
Endogenous pacemakers in this study; menstrual cycle. exogenous zeitgebers were stronger (pheromones) as the cycles were affected.
Contradictory evidence for line of argument: However, recent research by Trevathian et al carried out a more controlled investion using lesbian couples and found no evidence of menstrual synchrony.
Males also subject to monthly rhythms. Empson (1977) found evidence in males for a periodic variation in both body temps and subjective ratings of morning alertness, with a cycle length of approx. 20 days.
Seasonal affective disorder;
- Is an infradian rhythm, which occurs once a year
- Depressive condition, where people become depressed during the winter months (i.e. normal mood in spring, summer and autumn and depressed in winter) and recover during summer
- Research studies have shown that the hormones melatonin and serotonin are implicated in the disorder
- The more darkness, the more melatonin is produced and this interacts with other chemicals, leading to depression
- Whilst SAD has been explained in terms of being a natural outcome of infradian rhythms, it could be the consequences of a disrupted circadian rhythm, brought about by seasonal changes from summer to winter
- People may get up at the same time, but go to bed earlier because it is dark and circadian rhythms are consequently distrupted in a similar way to when suffering from jet lag
Real world applications:
The understanding of the role of darkness in SAD has led to effective therapies, especially phototherapy. This uses very strong lights in the evening and/or early morning to change levels of melatonin and serotonin. SAD sufferes have reported that daily use of such boxes is enough to relieve them of their feelings of lethargy and depression.
However, it has been suggested that this improvement may be due to a placebo effect since patients have also been shown to improve when a fake negative-ion generator was used to treat them (eastman et al 1998)
- rhythms of less than a 24 hours
- most relevant example comes from the sleep portion of the daily cycle of wakefulness and sleep, which is, of course, an example of a circadian rhythm
- when sleeping, we move through a number of cycles of sleep, each lasts about 90 mins
- there are 5 stages of sleep within every sleep cycle, stage 1-4 and REM (stage 5) (look on page 10)
- the 1st 4 stages of sleep are called NREM sleep (non rapid eye movement) and the 5th is REM sleep (rapid eye movement), because of the movement of the eyes behind closed eyelides
- the control of the sleep cycle involves a network of centres in the brain communicating through a variety of neurotransmitters
- some important elements involved in controlling sleep include the SCN and the pineal gland
- REM sleep is thought to reflect dreaming
- Dement and Kleitman (1957) were the first to demonstrate this link. they work p's during both REM and NREM sleep, and found that many more dreams were reported during REM rather than NREM sleep. However, their conclusion is open to question, since not all ps recalled dreaming when awoken from REM sleep, and some did recall dreaming when awoken from NREM sleep.
- Hobson and McCarley (1977) proposed that if this link between REM sleep and dreaming is established, dreams may simply be a psychological read-out of the random electrical signals typical of REM sleep
- Psychologists have also identified the basic rest-activity cycle (BRAC). This is a 90 min cycle of activity throughout the day (reflecting the 90 min sleep cycle)
- Friedman and Fisher (1967) watched the eating and drinking behaviour in a group of psychiatric patients over periods of 6 hours, and detected a clear 90 min cycle in eating and drinking behaviour.
Evaluation research into ultradian rhythm
- Ecological validity - this is an issue when investigating sleeping and dreaming since work is often carried out in a sleep lab, with people wired up to a machine, in a strange bed, knowing they are being watched so the environment is artificial and not like real life/bedroom.
- Internal validity - this is often increased when research is conducted in a sleep lab, using objective measures such as EEG, EOG and EMG readings.
- Patterns of sleep may be affected by a number of factors, e.g, age, gender, work, life events
- Some research may lack population validity due to the restricted nature of the sample. It is inevitable that only limited numbers of p's can be used in studies which involve sleep labs.
Endogenous pacemakers and exogenous zeitgebers
- Our biological rhythms have evolved for 2 reasons:
- In order to fit in with the cyclic changes seen in the outside world we need our own rhythms. This involves both endogenous pacemakers, which are internal or inbuilt body clocks, probably as the result of inherited genetic mechanisms, and exogenous zeitgebers, which are environmental stimuli or cues that play a vital role in regulating biological rhythms.
- Biological organisms are complex systems where lots of different chemical processes are going on. Endogenous pacemakers seem to help co ordinate these processes.
The Suprachiasmatic nucleus
The main endogenous pacemaker is a tiny cluster of nerve cells called the suprachiasmatic nucleus (SCN), which lies in the hypothalamus.
The SCN obtains information about light from the eye via the optic nerve, even when our eyes are shut. This info acts to adjust our circadian rhythm.
The SCN is a pair of structures, one in each hemisphere of the brain, and each of these is divided into a ventral and dorsal SCN. The ventral SCN is relatively quickly reset by external cues, whereas the dorsal SCN is much less affected by light and therefore is more resistant to being resett (albus et al 2005)
The SCN works by sending signals to the pineal gland, directing it to increase production of the hormone meatonin at night. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness.
research evidence for endogenous pacemakers
Stephan and Zucker (1971): removed the SCN from rats, finding that the usual rhythmic cycles of activity and sleep were abolished, suggesting that the SCN is the site of the pacemaker.
Morgan (1995) found that removing the SCN from hamsters caused their circadian rhythm to disappear, but when SCN cells were transplanted in, the rhythm returned, again showing the central role of the SCN as an endogenous pacemaker. (problems extrapolating data from animals to humans).
Yamakazi (2000) found that the circadian rhythms persist in isolated lungs, livers and other tissues grown in culture dishes not under the control of the SCN. This suggests that most cells and tissues of the body are capable of activity on a circadian basis.
eval for research ^
extrapolating findings from animals to humans - why is this problematic , validity etc
ethics of animal studies
The process of resetting the biological with exogenous zeitgebers is known as entrainment. The opposite of entrainment is free running. - where the biological clock operates in the absence of any exogenous cues.
- is the dominant zeitgeber in humans
- can reset the body's main pacemaker (SCN) and also reset other oscillators located throughout the body because the protein CRY (Cryptochrome) which is an important element in the way the body controls bodily rhythms, is light sensitive
- Much of what we do is socially regulated (e.g. bedtimes, meal times, getting up times) all of what is socially desirable to our age and circumstances
- Hence our daily rhythms are entrained by social convention
- Different parts of our body seem to produce their own oscillating rhythms and some of these are not primarily reset by light. E.g. the zeitgeber for cells in the liver and heart is likely to be mealtimes because these cells are reset by eating (davidson 2006)
- In the Arctic Circle, Luce and Segal (1966) found that people sleep on average for 7 hours even though it is light all summer long, implying that social cues act as zeitgebers here.
Real world applications
- Since light is the dominant zeitgeber, much research has focused on the impact of artificial lighting on biological rhythms. Boivin et al (1996) found that circadian rhythms can be entrained by ordinary dim lighting, though bright lighting was more effective.
- If dim lighting does reset the biological clock, then the fact that we live in an artificially lit world may have some negative consequences. For example Stevens (2006) suggests that exposure to artificial lighting disrupts circadian rhythms and thus disrupts melatonin production, this might ultimately explain why women in industrialised and well lit societies are more likely to develop breast cancer. (melatonin may be linked with breast cancer risk as less melatonin stimulates growth of certain types of breast cancer cells)
- Strong artificial lighting has also been used to reduce the symptoms of SAD.
- It can be seen that there is an adaptive advantage in animals having endogenous pacemakers reset by exogenous zeitgebers, keeping them in tune with seasonal changes, day/night changes etc.
Evidence regarding the effect of light on SAD and the role of pheromones in the sychronisation of the menstrual cycle can be interpreted as demonstrating the effects of exogenous zeitgebers.
- the biological approach
- real world application
- animal research
eval for endogenous & exogenous
- the interaction between the 2, ie is it appropriate to discuss either endogenous pacemakers without reference to external zeitgebers and vice versa?
- evidence to support or contradict the role of each
- evaluation of the evidence (e.g. animal studies in role of endogenous pacemakers may lack validity because)
- compared the biological approach (endogenous) with the potential impact of social factors (within exogenous zeitgebers) - might allow you to discuss reductionism
- free will/determinism
- practical applications
disruption of biological rhythms
A lot of A01 description is consequences of shift work and jet lag. A02 is how to minimise some consequences.
Distruption of biological rhythms
- Usually, exogenous zeitgebers change gradually, allowing time to adjust.
- However, rapid change disrupts co ordination between internally regulated rhythms and external exogenous zeitgebers, creating consequences for the ability to function properly.
- The synchrony of an organism with both endogenous pacemakers and exogenous zeitgebers is critical to well being and survival.
- In humans, a lack of synchrony within the environment might lead to health problems, such as those associated with jet lag, shift work and the accompanying sleep loss, e.g. impaired cognitive function, altered hormonal function and gastrointenstional complaints.
SHIFT WORK (see own notes on paper)
Shift work involves working at times when people are normally asleep, and sleeping when others are awake. This causes a breakdown in the usual co ordination between endogenous pacemakers and exogenous zeitgebers. Some of the effects of this disruption are:
- Decreased alertness - nightworkers often experience a circadian 'trough' of decreased alertness during their shifts (Boivin et al, 1996). This happens between midnight, when cortisol levels are lowest, and 4am, when core body temp is at its lowest.
- Sleep deprivation - workers who have to sleep by day often experience sleep problems due to sunlight, noise, family responsibilities etc. Daytime sleep is typically 2 hours shorter than night time sleep, with REM particularly affected. (Tilley and Wilkinson, 1982). Such poor quality sleep mkes it even more difficult for workers to stay awake during the night.
- Effects on health - there is a significant relationship between shift work and organ disease. E.g. Knutsson et al (1986) found that an individual who has worked shifts for more than 15 years were 3 times more likely to develop heart disease than non shift workers. Martino et al (2008) linked shift work to a range of organ diseases incl. kidney disease. This may be due to the direct effects of desynchronisation or indirect effects such as sleep disruption.
- Social disruption - divorce rates for example may be as high as 60% among all night shift workers (solomon 1993)
Shift work may be non-fluctuating (eg a stable night shift from 11pm to 7am) or fluctuating (3 different rotating 8 hour shifts). These types of shifts have different effects: non fluctuating shifts allow the body to adapt, fluctuating shifts intensity the severity of circadian rhythm disturbance.
Colligan et al (1978) found that workers with shift rotations had more accidents than workers on set shifts. they also drank more alcohol, took more sleeping tablets, had digestive disorders, colds, anxiety, tiredness and less successful social relationships, demonstrating the destructive consequences of disrupting biological rhythms.
- term 'jet lag' is generally used to refer to the physiological effects of disrupted circadian rhythms - even those that do not arise from jet travel.
- our biological rhythms are not quipped to cope with sudden and large changes: it's estimated that the dorsal portion of the SCN takes several cycles to fully resynchronise to abrupt large changes in environmental time - this is why it's called jet lag.
- Winter et al (2008) calculated that this is equivalent to 1 day to adjust to each hour of time change.
- Symptoms of jet lag: loss of appetite, nausea, fatigue, disorientation, insomnia and mild depression.
- Jet lag is worse travelling WEST to EAST, as it is easier to adjust biological clocks if they are ahead of local time (phase delay) than behind (phase advance). This view was confirmed by Klein et al (1972) working with travellers between the US and Germany and by Schwartz et al (1995) studying baseball teams travelling either west -> east or east -> west to play league games. The eastern US teams played better when travelling West, than the Western teams when travelling East. However, this may be that the Eastern teams were just better.
Reducing the harmful effects of shift work & jet l
- Adjusting eating - recent research suggests that a period of fasting followed by eating on the new time schedule should help entrain biological rhythms (fuller et al, 2008), possibly because some of our body clocks are reset by food intake.
- Melatonin - Herxheimer and Petri (2001)) reviewed 10 studies and found that when melatonin was taken near to bedtime, it was remarkably effective in adjusting sleep patterns. However, if taken at the wrong time of day it may actually delay adaptation.
- Planned napping during shifts - although this has been shown to reduce tiredness and improve performance (Sack et al, 2007) it is not popular with employers or employees.
- Rotating shifts - research shows that fluctuating shifts are likely to be more disruptive than non-fluctuating shifts, forward-rotating shifts which follow the logical order of the day may be easier on the body and less damaging to worker health, according to Bambra et al (2008). E.g. of such a shift pattern would be a shift in the morning for 1 week, then an afternoon shifts for the next week, and finally a night shift for the 3rd week. Bambra also concluded that rotating workers through shift changes more quickly (every 3-4 days, instead of 7) is better for health and work life balance.
- Staying awake to local time - helps entrain rhythms.
- gender bias - research into shift work has involved male p's. findings may be considered to be gender biased with the results not necessarily being representative of females
- practical applications - research findings have led to the implementation of systems to rotate shifts forward to reduce the negative effects; melatonin supplements to reset the internal body clocks of shift workers and those suffering from jet lag; and other things such as adjusting mealtimes to fit new circumstances.
Czeisler et al (1982)
first discovered the benefits of forward rotating shifts.
carried out research at utah chemical plant, where workers used the traditional backwards shift rotation with 7 days on each rotation
they found high illness rates, sleep disorder and elevated levels of stress which led them to the conclusion that the workers' internal body clocks were out of sync with exogenous zeitgebers
they made the management move to a phase delay system of rotating shifts forward in time to reduce negative effects. (6am-2pm, 2pm-10pm; 10pm-6am). Shift rotations were also adjusted to every 21 days instead of 7. giving time for adjustment
when they re assessed the workers 9 months later they found that workers appeared healthier, more content and output was up.