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Biological rhythms
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Some practical notes of advice: The possible questions on this topic are limited and will most likely be along the lines of: Discuss two types of biorhythm or Discuss what psychological research has told us about biorhythms or Discuss the roles played by endogenous (internal factors) and zeitgebers (environmental factors) in determining bodily rhythms. Criticisms of theories or research is limited so evaluation marks are going to be obtained by comparing studies and highlighting how they show different things or combine to produce a more complete picture of the mechanisms involved.
Introduction Most human and non-human animal functions are cyclic, alternating over a period of time. Obvious examples include the sleep-wake cycle which repeats over a 24 hour cycle, or the hibernation patterns of some creatures that typically rest through the winter months and awaken in spring. The major debate, similar to the nature/nurture in some respects, but without the controversy, is to what extent biological rhythms are determined by internal clocks (endogenous factors) and by environmental factors (so called zeitgebers).
Order of play:
Types of biorhythm Circadian Variation is over an approximate 24 hour period. The word stems from the Latin; circa (meaning ‘about’) and diem (meaning ‘day’). There are some cycles that we are consciously aware of; the sleep/wake cycle being an obvious one, but most cycles we are not usually aware of. For example our core body temperature fluctuates over a 24 hour period. Generally it peaks mid afternoon at about 37.1 C and troughs in the wee small hours at about 36.7 C. This may not sound like a lot but you may nevertheless have noticed the effect and found yourself shivering unexpectedly as you’ve walked home after a late night party, even in August! Other examples of human circadian rhythm include heart rate, metabolism and breathing. These follow a similar pattern to temperature, which may not seem surprising, since they match our patterns of activity. However, people on shifts, who are sleeping through the day and more active at night still keep the same circadian rhythms with body temperature, metabolism and resting heart rate still peaking mid afternoon! Blood clotting also shows a circadian rhythm, peaking in the morning and coinciding with increased incidence of heart attack It is worth mentioning that there are big differences between individuals. The most noticeable being the larks/owls division; larks being morning types and owls preferring the evenings. Typically when studied larks seem to be clock advanced having rhythms about two hours ahead of owls.
Ultradian These occur more than once in a 24 hour cycle. Most are confined to either day or night, for example the stages of sleep. As you should be aware, a typical night’s sleep takes you from stage 1 to 4 then back to 2 and finally into REM. This whole cycle then repeats itself three or four more times during the night, each cycle lasting about 90 minutes. There are a number of similar cycles during the daytime too. Sometimes these are referred to as diurnal. Examples include eating (approximately every four hours), smoking and drinking caffeine (in those addicted), and urination. Infradian These occur over a period of time greater than 24 hours. In humans the best examples are menstrual cycle and PMS (Pre-Menstrual Syndrome) which occurs a few days prior to the onset of bleeding and is characterised (information for the boys), by loss of appetite, stress, irritability and poor concentration. There are a number of rhythms that are cyclic over about one year. A human example would be SAD (Seasonal Affective Disorder), more on this later; and in the animal world migration, mating patterns and hibernation of some species.
Endogenous There is plenty of evidence to suggest that our biological rhythms are inherited. For example although within a species there is variation of rhythm, each individual tends to have a pattern of rhythm that shows little variation over a lifetime. Even the most extreme of environmental factors such as anaesthesia (not the late Russian Princess), alcohol and drug abuse, brain damage and loss of consciousness have little effect on our rhythms. To study endogenous clocks it is necessary to isolate people from external cues for many months. The most famous case of this was in 1972 when the French geologist Michael Siffre stayed in a cave for seven months (time spans vary), with adequate food and drink, exercise equipment and a permanently manned telephone line to the outside World. However, Michael received no clues as to the time of day. The cave was illuminated only by artificial light which he controlled. Over a period of time his body clock moved form a 24 hour cycle to a 25 hour pattern. In practice this meant that he was going to bed about one hour later each day. So, after 12 days in the cave he would be going to sleep around midday and waking late evening. After three weeks he would have lost a day! Schocter et al (1997) found that we are most likely to feel sleepy in the late evening (ground breaking or what!). They called this the ‘sleep gate.’ This was preceded 2 hours earlier by an increase in melatonin production suggesting that this chemical triggers sleepimess. In an attempt to find the endogenous clocks’ period volunteers have been exposed to severe variations in clock alteration, for example, exposing participants to artificial lighting simulating a 28 hour day. (So if ‘sunrise’ was at 6am on day 1 it would be at 10am on day 2 and so on). The body cannot adjust to such extremes and the body clocks ‘run free.’ In all cases the cycle is greater than the usual 24 hours but estimates vary as to the exact length. Some put the increase at as little as 12 minutes whereas others claim one hour. The biological rhythm often comes into conflict with external cues, however, although disruption may occur the cycle remains intact. If you have ever stayed up all night at a party and walked home in the early hours you may have felt cold, perhaps getting the shivers, even though it was August. This is your natural dip in body temperature still occurring despite the night’s activities.
Biological basis of circadian rhythms In lower species the pineal gland appears to be the brain structure responsible for regulating bodily rhythms, especially the sleep/wake cycle. The pineal gland lies at the top of the brainstem and in lower species this means it is close to the surface of the skull. As well as having an inbuilt cycle it also has light sensitive cells that receive information through the skull about external light levels and these seem to keep it synchronised with fluctuating environmental conditions. The pineal gland secretes melatonin which is known to have an influence on sleep patterns. In humans the pineal gland is still situated in the same place, at the top of the brainstem, but we have an extensive cerebral cortex overlying this. (When I say ‘we’ I refer to most of us!). This means the pineal gland is situated deep inside the brain so has no direct contact with conditions outside. (In fact the Greeks considered the pineal gland to be a possible site for the ‘soul’ since it was situated in the centre of the brain). In humans the suprachiasmatic nuclei (SCN) appears to take over the role. This is situated in the hypothalamus and just behind the eyes and receives sensory input about light levels through the optic nerve. The SCN then appears to regulate melatonin production from the pineal gland. Evidence suggests that there is more than one internal clock. Damage to the hypothalamus of squirrel monkeys alters their sleep/wake cycle but leaves other cycles such as metabolism and temperature unaltered, (Fuller et al 1981).
The SCN may regulate other cycles. Rusak & Morin (1976) found that lesions to the SCN disrupted their breeding pattern. Instead of just producing testosterone during the mating season, the hamsters produced it all year round. Morgan (1995) removed the SCN from some hamsters and found that their rhythms ceased. However, when they received SCN transplants from other hamsters the cycles were re-established. In a follow up they transplanted the SCN from mutant hamsters (15 feet long!) who had shorter circadian rhythms. The hamsters receiving these SCNs developed these mutant cycles. (However, they did not grow to the same length!).
Mutant hamsters have been used as a green source of electrical energy in London. Using the London Eye as a giant wheel they can generate enough electricity to power Westminster and the half of Kensington!
Its role in the breeding cycle of humans is not so clear cut. We do know however, that light levels can influence the menstrual cycle. The menarche (onset of menstruation) is more likely to occur in the winter months and generally occurs earlier in girls that are blind. In Finland, during its very long summertime daylight hours, conception rates increase significantly. Perhaps you can think of other contributory factors! No football for example? External Factors (zeitgebers) Light appears to be crucial in maintaining 24 hour cycles: Campbell & Murphy (1998), in a bizarre experiment, shone bright lights onto the back of participants’ knees and were able to alter their circadian rhythms in line with the light exposure. The exact mechanism for this is unclear, but it seems possible that the blood chemistry was altered and this was detected by the SCN. Miles et al (1977) reported the case study of a blind man who had a daily rhythm of 24.9 hours. Other zeitgebers such as clocks, radio etc. failed to reset the endogenous clock and the man relied on stimulants and sedatives to maintain a 24 hour sleep/wake cycle. Luce & Segal (1966), however, have shown that light levels can be over ridden. In the Arctic Circle people still maintain a reasonably constant sleep pattern, averaging 7 hours a night, despite 6 months of darkness in the winter months, followed by six months of light in the summer. In these conditions it appears to be social factors that act to reset endogenous rhythms rather than light levels. Conclusion Our biological rhythms therefore appear to be internally and externally controlled. Left to their own devices our internal clocks seem to be set to about a 25 hour cycle but external cues, especially light, resets our clocks daily. So why do we need internal and external control? If control was entirely internal we would not be sensitive to external changes such as light levels. Species that hibernate or migrate would not adjust their behaviour. If control was entirely external our rhythms would be too erratic and change day to day depending on weather conditions etc.
Seasonal Affective Disorder (SAD) Although it is apparently normal for most people to feel more cheerful in the summer months than in winter, a small number of people suffer an extreme form of this that appears to be related to the lack of bright light in the winter months. Since this cycle repeats itself over a period of one year it is classed as a circannual rhythm (a variation of infradian). As hopefully you’ll remember from the stuff we did on the physiology of sleep, light levels, as detected by receptors in the eye, influence levels of melatonin and serotonin. Additionally as you will hopefully recall from your work on depression, serotonin is implicated in mood. See how eventually all these strands knit together! At night low light levels stimulate the production of melatonin, this is what triggers sleepiness. Therefore you would expect the lower light levels of the winter months to have a similar affect.
Research evidence The symptoms of SAD can be reduced in polar regions by sitting patients in front of very bright artificial lights for at least one hour per day. This lowers the levels of melatonin in the bloodstream which in turn reduces the feelings of depression. The precise mechanism for this is still unclear, it could be that melatonin (released from the pineal gland) has a direct affect on mood or it could have its influence indirectly through serotonin. Drugs used to treat depression such as Prozac and other MAOIs (monoamine oxidase inhibitors), appear to work by altering serotonin levels. Eastman et al (1998) have found that bright light treatment at any time of day can be beneficial, however, it is most effective in the morning. The researchers conclude that bright light administered in this way may be acting as a zeitgeber and resetting the body clock in the morning.
The menstrual cycle Obviously a cycle that lasts about one month, so this cycle is infradain. Like other rhythms, the menstrual cycle appears to be under the influence of both internal (endogenous) mechanisms, and external zeitgebers. It is worth reminding you that menstruation itself, usually considered to be the start of the cycle, is in fact the termination of the cycle! Endogenous control The cycle is under the internal control of hormones, particularly oestrogen and progesterone, secreted by the ovaries. These cause a number of physiological changes within the body including the release of at least one egg (ovum) from the ovaries and the thickening of the lining of the womb (uterus), in preparation for the arrival of the egg. If the egg is not fertilised then the lining of womb is shed and menstruation occurs. The contraceptive pill mimics the effects of pregnancy and cons the body into ceasing production of further eggs. External control (zeitgebers) It has long been known that the menstrual cycle can be influenced by external factors, most notably by living with other women. The most likely mechanism for this is by the action of pheromones, chemical substances similar to hormones but which carry messages between individuals of the same species. Russell et al (1980), in a classic study, placed dabs of sweat taken from the arm pits of sexually inactive women and placed on the upper lips of other women. Four out of five of the women had menstrual cycles that had synchronised to within one day of the sweat-donor. Reinberg (1967) reported the case of a young woman who lived in a cave for three months with the only light being provided by a miner’s lamp. The woman’s daily cycle lengthened to 24.6 hours, (compare to Michael Siffre) and her menstrual cycle shortened to 25.7 days. It took a year before her cycle returned to normal! Reinberg believed that light levels could therefore influence the period of the cycle (no pun intended!). This theory is backed by research on 600 German girls (no armpit jokes), which found that the onset of menstruation (menarche) is more likely in the winter months when light levels are low. Timonen et al (1964) found that women were far more likely to conceive in lighter months of the year than in darker months. This was attributed to the effects of light on the pituitary gland, which exerts its influence on the cycle via the ovaries.
Evolutionary advantages of external control of the menstrual cycle Bentley (2000) believed that synchronisation between women living in close proximity would ensure that the women would conceive and give birth at similar times. This would be beneficial since they could share breast feeding, a behaviour observed in other species. Similarly, McClintock (1971) found that women who work in a mostly male environment have shorter menstrual cycles. In the past this would be of evolutionary advantage since it would provide more opportunities for pregnancy. Evaluation Evidence from physiological methods is objective (e.g. for synchronisation etc.). The research can be explained in evolutionary terms which gives added meaning and validity to the findings. Unfortunately much of the evidence is from case studies, so as a result is based on relatively small sample sizes. This means it is difficult to generalise to the population as a whole.
Pre-menstrual Syndrome (PMS) This is a collection of symptoms that usually occurs four or five days before menstruation. Typically symptoms include irritation, depression, headaches and a decline in alertness. Other possible symptoms, according to Luce (1971) include insomnia, cravings for certain foods and even nymphomania! However, it is the psychological affects that have been most widely studied. Dalton (1964) alarmingly reported a sharp increase in crimes, suicides, accidents and a decline in schoolwork associated with PMS. More recent studies have played down these findings, for example Keye (1983) concluded that although a small minority of women may suffer in this way, such extreme symptoms are relatively rare. PMS appears to have an underlying physiological cause, as evidenced by the fact that it is reported in all cultures. This is contrary to earlier theories that attributed it to cultural factors and a denial of femininity! Janiger reported similar symptoms in other primates.
Disruption of biorhythms
In some respects biorhythms are like stress in that they developed in response to situations we found ourselves in hundreds of thousands of years ago. Like stress, our body’s in built and inherited biorhythms are outdated in a modern world that has a 24 hour culture. In normal circumstances our in-built body clocks are not in conflict with external zeitgebers. The daily pattern of life, waking in the morning at or around sunrise, working through the day when our metabolism, body temperature etc. are at their peak and going to sleep at night when it gets dark, causes no disruption. However, given modern life there are situations now when our internal clocks do come into conflict with external cues, such as dark/light. The two most obvious examples are shift work when we operate on a rotating schedule of hours and jet lag when we travel across time zones either east to west or west to east.
Jet lag Suppose you leave London Heathrow at 6pm (GMT). The flight to New York JFK will take about six hours. However, because time on the east coast of America is five hours behind you will arrive at 5pm local time. However, your body clock assumes that its midnight since the flight has taken six hours. As a result your internal clock is ready for bed, your temperature is starting to fall and your metabolic rate is slowing. External cues however, are telling you something quite different, its still light, people are still shopping, the roads are still busy etc. To overcome this conflict between internal and external effects is not difficult. Provided you keep yourself well stimulated for the next five or six hours you should be able to stay awake ‘til 11pm local time (4am body clock time) and adapt to the new time zone.
But, suppose you leave JFK airport in New York at 12 noon (Eastern standard Time) heading for London Heathrow. The flight is six hours. You arrive in London at 6pm (New York Time) but this is 11pm GMT (London time). Are you with me so far? Your endogenous clock has just lost five hours! Your body clock still thinking it’s only 6pm, is not ready for bed. Your body temperature, metabolism etc. is still at its peak. To adapt to the new time setting you must now go to bed! This is not so easy as going east to west. Going to sleep when you are wide awake is not as easy as staying awake when you’re tired. As a result flying east to west is more troublesome and takes longer to adapt.
Shift work This is usually more troublesome than jet lag since it involves prolonged conflict between internal clocks and external stimuli. As a result during the day when metabolism etc. is at its peak the person is expected to sleep. At night when body temperature etc. are low the person is expected to be working. This situation is often compounded by 1. the person reverting to ‘normal’ sleep/wake cycles at the weekend and 2. shifts altering from one week to the next. As a result the person never adapts to a new rhythm, leaving their biorhythms in a permanent state of desynchronisation!
Shift work results in:
In the very least this can result in reduced productivity and reduced employee morale. In extreme cases it can have catastrophic consequences. Major disasters such as Chernobyl and Three-mile Island, Bhopal (explosion at a chemical plant in India), Exxon Valdez (oil tanker spillage in Alaska and many other major incidents have occurred in the early hours of the morning and been attributed to tiredness. Additionally on the roads in Britain there are a disproportionately high number of fatal accidents in the early hours of the morning. Shifts can follow a number of patterns:
Research by Charles Czeisler has found that the best shift pattern is one that surprisingly rotates rather than is fixed, changing the shifts forward or clockwise rather than backwards, and having a slower period of rotation for example over a period of 18 days or more. Czeisler et al (1982) were called in to sort out shift related problems at a chemical plant in Utah, USA. Having implemented the changes suggested above a number of benefits were reported. These included greater productivity, fewer accidents, increased morale and improvements to the health of workers. It is worth mentioning that work by Monk & Folkard (1983) reported that rapidly rotating shifts (i.e. working no more than 2 days on any one shift) were preferable to slower rotation of shifts. This seemingly contradicts the work of Czeisler.
Stages of sleep This section fits logically into both the ‘biorhythms’ and the ‘sleep’ sections of this particular topic area. As far as our set text is concerned its rightful place is in ‘sleep’ but I see no reason why it could not be used as an example of a biological rhythm. Sleep is the perfect example of an ultradian rhythm, that is, one that repeats itself over a period of less than 24 hours. The cycle of sleep typically lasts about 90 minutes and during a typical nights sleep we will repeat this cycle four or five times. History I know that Henry Ford said that this was ‘bunk’ but the history of sleep is useful from the point of view of research into the stages of sleep. Until the 1930s there was no scientific or objective way of measuring what was happening in the brain. Following the invention of the electroencephalogram (EEG), it became possible to record the electrical activity of the brain. This was crucial, since as you should be aware by now, the activity of the brain is mainly electrical in nature. 1937: Loomis et al discover that during sleep the waves generated by the brain slow and become larger. For the scientists amongst you, the frequency falls as the wavelength increases. 1952: Aserinsky was checking to make sure that his newly acquired EEG was working properly. He placed the electrodes of the machine near to the eyes of his eight year old son, Armond whilst he was asleep. At regular intervals he noticed that there were bursts of electrical activity. 1953: Aserinsky & Kleitman coin the phrase ‘Rapid Eye Movement’ or REM. 1957: Dement & Kleitman realise that there appears to be a link between REM sleep and dreaming. They tested 5 participants, waking them either 5 or 15 minutes into periods of REM sleep. Participants would normally report dreams and the length of the dream would correspond to the time that they had spent in REM. 1968: Rechtschaffen & Kales record four other distinct stages of sleep.
All this is important because prior to the 1930s it was assumed that sleep was sleep. Nobody even considered the possibility of different stages or patterns of activity.
AwakeThe brain is obviously active and shows what is called beta activity (see EEG above). When we relax, for example close our eyes or meditate the brain shows alpha activity. These are slower waves with higher amplitude. Stage 1 sleep (15 minutes) This occurs at the start of a nights sleep. It lasts a matter of minutes and you will all be familiar with it since we often wake from this stage. For example sat watching ‘Big Brother’ gradually losing the will to live or certainly to stay awake, we may nod off. We may wake from this stage and think that we’ve been dreaming. In fact these hallucinations are referred to as hypnogogic phenomena and usually comprise fleeting images rather than the bizarre stories more characteristic of dreaming. The eyes may roll slowly. Sometimes we may wake without realising that we’ve even nodded off. Brain waves are slower and are called ‘theta.’ Other times we may wake with a jerk or knee twitch. Stage 2 sleep (20 minutes) After about a minute or so we enter stage 2. This is characterised by bursts of high frequency waves called ‘sleep spindles.’ We are still aware of sounds and activity around us and the brain responds to this with K-complexes. At this stage we are still very easily woken. Stage 3 sleep (15 minutes) The brain waves start to slow and become higher in amplitude and wavelength. These are called delta waves and are associated with deep sleep. We are now more difficult to wake. First time round in the night this stage is brief, only a few minutes, but we spend longer in it later in the night. Stage 4 sleep (30 minutes) In many respects this is a continuation of stage 4, however, delta waves now constitute most of the brain activity and we are now at our most relaxed. At this stage we are very difficult to wake up and even vigorous shaking may not be sufficient to wake some people, me included. However, a quiet but meaningful sound such as a baby crying can be sufficient, again indicating that the brain still retains some degree of awareness to external stimuli! Heart rate and blood pressure fall, muscles are very relaxed and temperature is at its lowest. We have now been asleep for about an hour. We start to ascend back through these stages in reverse order, i.e. back to level 3 and then to level 2. However, instead of going back to level 1, after just over an hour we enter a very bizarre state of consciousness.
REM sleep (10 minutes at start of night, up to an hour later in the night) Sometimes referred to rather unimaginatively as stage 5, or more descriptively ‘paradoxical sleep.’ REM is strange. The brain now becomes very active, almost indistinguishable from a waking brain. Remember the activation-synthesis theory of dreaming? The pons in the midbrain throws out bursts of electrical activity into the cortex lighting it up like a Christmas tree. Heart rate and blood pressure increase, as does body temperature, and the eyes twitch rapidly giving this stage its name. But, despite this frantic activity the body remains motionless, cut off from the brain by the pons. We are paralysed and unable to act out the brain’s bizarre thoughts. REM is now thought by some to be the deepest stage of sleep since it is now that we are most difficult to wake up. However, this could be as a result of being so absorbed in our dreams. Paralysis appears to be to prevent the body acting out our dreams and endangering our lives. Cats that have had lesions to the pons do in fact appear to act out their dreams. Remember, however, that we have no certain way of knowing whether lower species do dream; it is merely assumed that they do because all warm blooded creatures (birds and mammals), with the exception of the very early egg-laying mammals, have REM sleep. Our first visit to REM typically lasts about for about 10 minutes and we start our journey back down to stage 2, stage 3 and stage 4 sleep. This cycle repeats throughout the night, however, as the diagram below illustrates, we spend most of the first half of the night in deep sleep (slow wave or NREM), and most of the second half in REM sleep.
The last cycle is referred to as the ‘emergent cycle’ since it is during this one that we wake up. This last cycle contains no stage 3 or stage 4 sleep so under normal conditions we will emerge from either REM or stage 2 and the waking process may be accompanied by further hypnogogic images as was mentioned in stage 1. (Strictly speaking on waking these are referred to as hypnopompic). The outline above describes a typical or average night’s sleep. Obviously there are large individual differences between people. Some may sleep much shorter periods, others who have been sleep deprived will spend longer in stage 4 and REM, and the pattern changes with age. Changes over a lifetime The infant child sleeps much longer than an adult. In the first year of life a child will typically spend about 16 hours asleep, half of this being in REM. By the age of one this has dropped to about 12 hours of total sleep with about four hours of REM. By the time we have reached maturity we usually sleep for 8 hours with only one quarter (2 hours) being spent in REM. Note, people who sleep longer tend to spend much of the extra time in REM. As a species, in the West we sleep less than we did a century ago. It is estimated that in the UK we now spend only 7.5 hours asleep per night compared with 9 hours in Victorian times. As we get older still there are further changes. REM continues to decrease, and by the time we reach 60 stage 4 is almost non-existent. As a result older people are more easily awoken and often complain of insomnia. In fact it just appears that we need less sleep as we get older, a possible clue to the function of sleep. Hope you found this interesting. I quite enjoyed writing this section. As I said you could incorporate this information into a question on sleep research or a question on biorhythms. Even if you have no opportunity to use it, I’m sure that you could bore friends with it endlessly at parties! Sleep research Evaluation of
All birds and mammals sleep and other creatures have a dormant period during the 24 hour cycle, suggesting that sleep must perform some vital purpose. However, in humans the amount of sleep needed by individuals does show considerable variation. Meddis (1979) reported the case of a woman who only slept for one hour per night but showed no ill effects. This case however is unusual and it is estimated that in the UK with an average of 7.5 hours sleep per night, that most of us are in a state of mild sleep deprivation. Sleep deprivation studies highlight the need for sleep to maintain normal levels of awareness and cognitive ability as well as psychological health. Three or four nights without sleep can result in symptoms of mild paranoia and hallucinations. Yet, even in the most extreme cases, such as Randy Gardner’s eleven nights without sleep, the effects are not long lasting. Why then do we sleep, and why do we spend almost one third of our lives in this state of reduced consciousness? There are two main theories: Evolutionary theories: · Sleep helps to protect us from harm at night · Sleep helps us to conserve energy Restoration: · Sleep helps us to repair damage done to our bodies during the day · Sleep restores the brain’s levels of neurotransmitters The following theories are attempts to explain why we sleep rather than why we dream. Evolutionary theory concentrates on slow wave or NREM sleep and makes little or no attempt to consider REM sleep. Restoration theory on the other hand tackles both. However it makes no attempt to explain dream content. Therefore it is not suitable to include in an essay on dreaming.
Evolutionary (ecological) theory
‘The lion and the lamb shall lie down together but the lamb will not be very sleepy!’ Woody Allen (from Love and Death)
1. Protection (Meddis 1975)
In our evolutionary past night time would have been a time of great danger. Since as a species we have poor night vision we would have been unable to forage, likely to fall and hurt ourselves and wide open to predation from species with better night sight. Sleep would have been an evolutionary advantage since it would have kept us out of harms way. As a result, those members of the species that slept would have been more likely to have survived to maturity and passed on their genes, ensuring that as an activity, sleep would have been retained in our behavioural repertoire. The theory also considers the metabolic rates of other species, predicting that animals with high metabolic rates will need to spend more time eating so have less time to sleep. Animals such as the shrew are safer since they have a burrow to return to, but due to their high metabolic rate and need to be eating regularly only have time to sleep for two hours. Larger preyed-upon species, e.g. ground squirrel, have burrows where they are safe, similar to the shrew, but since they are larger and have a lower metabolic rate, they need to eat less often and so can spend longer tucked away in their burrows asleep. However, there are some glaring anomalies. On the face of it you would expect species most at risk to sleep longer (in order to get added protection) but often the opposite is the case. Species most at risk such as herbivores sleep least (a few hours a day in brief naps), whilst species that are at little risk such as big cats sleep for most of the day! Some texts appear to think this actually supports Meddis’ theory but I really can’t see how!!
Other obvious evaluation comments If the only purpose of sleep is to protect from harm, then why do species that face the most risk when asleep bother to sleep at all. Surely it would make more sense to stay awake and alert to danger. Evans (1984) sums it up nicely: ‘The behaviour patterns involved in sleep are glaringly, almost insanely, at odds with common sense.’ Sleep can also be dangerous in other respects as these two dolphin examples illustrate: · The Indus dolphin is at constant risk from being hit by logs and other big river debris being swept down the River Indus. Clearly, loss of consciousness is life threatening since it means loss of vigilance. However, despite this it still grabs quick naps of a few seconds at a time. In effect, this dolphin is risking its life to sleep. How can this be protective? · The Bottlenose dolphin sleeps with one hemisphere of its brain at a time so it can remain partly conscious and return to the surface to breathe. Summarizing Meddis Animals sleep for short periods if: 1. They high metabolic rates so need to be constantly eating. 2. They are likely to be eaten.
1. They have low metabolic rate so eat less and therefore have more time available to sleep. 2. They have no natural predators.
2. Conservation of energy (Webb)
A variation on Meddis is the Hibernation Theory which is also sees sleep as an adaptive behaviour, but this time designed to conserve energy. It compares sleep to hibernation. During hibernation body temperature falls and the animal becomes inactive as a way of conserving energy when food is scarce. The more at risk we are from predators the longer we will sleep. Other factors will also effect the time spent sleeping, for example the time we need to spend each day searching for food. Again, in the case of early human species night time would have been an unproductive period when we would have been unable to forage. Sleep would have been one way of conserving our resources by lowering our metabolic rate.
Humans will still sleep due to evolutionary hangover from the days when we were vulnerable. Children (babies) sleep longer to protect mothers from exhaustion (What about fathers? Ed.)
Evaluation of conservation theory Meddis criticises the theory on the grounds that it is over-simplistic. According to Meddis (as seen above), the amount of time spent sleeping is a compromise between protecting from danger and dietary requirements.
In fact sleep provides little in the way of conservation of energy. Just being inactive at night would save almost as much energy but without the added danger of loss of vigilance. It is estimated that the calories we save by sleeping rather than simply resting, is equal to the calories in a slice of bread!
Evaluation of evolutionary theories in general
· If sleep serves no other purpose other than safety, why do we suffer psychological problems when deprived of sleep and why as Rechtschaffen found in rats do animals die without sleep. · Empson (1993) describes sleep as ‘a complex function of the brain involving far reaching changes in body and brain physiology’ adding that it must have some restorative function. He famously refers to the evolutionary theories as ‘waste of time’ theories as they see sleep merely as a way of passing time. · In an attempt to explain REM in evolutionary terms it has been suggested that active sleep is most prominent in birds and mammals - both warm-blooded. Perhaps REM keeps brain active and prevents it dropping to dangerously low temperatures. · If sleep is designed to make us inconspicuous at night, why do we snore! · Evolutionary theories are unable to explain the complexities of sleep. For example why do we have five stages of sleep (including the very bizarre REM stage)? Finally, some have argued that sleep would now be pointless in most human societies because we are much more advanced and able to protect ourselves against harm at night. However, as already pointed out, our change in behaviour as come about very quickly (in evolutionary terms), particularly with the discovery of electricity. Evolution of biology and physiology on the other hand is much slower, so we wouldn’t expect to see big changes in our sleep pattern for hundreds of years at least.
Oswald (1966) suggested that sleep restores depleted resources of energy, removes waste from muscles and repairs cells. For example during the day waste chemicals build up in the muscles following physical exertion and neurotransmitters used for communication throughout the nervous system are likely to be used up. Sleep therefore might be an ideal time for the body to remove this waste and restock/replenish its levels of neurotransmitters in preparation for activity the next day.
In addition the body could carry out repairs to damaged cells and growth could occur the young.
Non REM sleep According to Oswald, NREM sleep is a time for replenishing the body. Oswald points out that most NREM sleep, especially stages 3 and 4, occur at the start of the night when the body is most tired. During stages 3 and 4 we secrete greater levels of growth hormone into the blood which would help in the repair process, seeming to offer support to his theory. (Good evaluation phrase!). We do know that many restorative functions appear to occur during sleep, for example digestion, removal of waste from muscles etc. and protein synthesis for repair and growth. However, these processes also occur whilst we are awake too!
Further support is provided by Shapiro (1981) who studied ultra marathon runners who had completed a 57-mile run. It was found that they slept for 90 minutes longer than usual for the next two nights. REM sleep decreased whilst stage 4 of quiet or NREM sleep increased dramatically from 25% of nights sleep to 45%.
REM sleep Oswald (1980) and Hartman (1984), built on the theory to include restoration during REM sleep. They believe that REM is for restoration of the brain. Stern & Morgane (1974), believed that neurotransmitter levels within the brain may be restored during REM sleep. The young brain is growing and developing at its fastest rate so young children, especially babies sleep for much longer than adults. In the newborn about 9 hours a day is spent in REM compared to about 2 hours in adults.
It is important to remember that this seeks to explain the biological state of REM sleep and makes no mention of the psychological state of dreaming. Therefore it is not to be used in a question that asks for theories of dreaming.
Research in support of restoration theories
The most obvious support comes from aspects of the sleep deprivation studies to be discussed in the next section. First some other evidence:
· Disruption of stage 4 sleep can cause fibrositis, a condition of the lower back caused by muscle wasting. · Growth hormone, essential for production of amino acids and proteins is secreted during deep sleep. · Babies sleep for much longer than adults and spend up to 9 hours in REM. This would allow time for growth and development of the brain. · Following brain insults i.e. damage caused by ECT, strokes, drug overdoses etc. Patients spend longer in REM for an average of 6 weeks. This suggests time is being spent carrying out repairs by laying down new proteins and building new tissues. · It has been suggested that neurotransmitters are replenished during REM. When patients are prescribed antidepressants e.g. tricyclics or monoamine oxidase inhibitors (MAOIs) they spend less time in REM.
 
· According to Oswald and Horne loss of these neurotransmitters would explain problems in perception memory and attention experienced following sleep deprivations e.g. Randy Gardner and Huber-Weisman (1976)
Research against restoration theories
· Protein synthesis occurs 24 hours a day, not just during stage 4 - although it does seem to peak in stage 4. · Amount of sleep does not appear to decrease when our level of daytime activity decreases, (as shown by Ryback & Lewis, and others). · Following great physical exertion the amount of additional sleep we need may only be negligible. Horne & Millard (1985) found that although we usually fall asleep quicker we do not usually sleep for longer. · The brain is very active during REM so runs counter to the idea that it is an ideal time for repair. · The model is over simplistic since in fact neuro-chemicals appear to be produced throughout a night’s sleep and not just during REM.
Other research contradicting the theories Returning briefly to animal studies; this theory predicts that more active species will sleep longer. However, one of the least active creatures, hence its name, the sloth, sleeps for about 20 hours a day, whereas some very active humans get by on a few hours only.
One final comment on this section that is always worth making: Horne (1988) distinguishes between core and non-core sleep. Core sleep (stages 4 and REM) appear to be essential and present in all species, whereas non-core sleep (stages 2 and 3) appears not to be so vital. Evidence for this is: following sleep deprivation we spend longer in REM and stage 4 suggesting that we need to catch up on these.
These are interesting in their own right, but from a practical point of view can be used: 1. As evidence for the restoration theory of sleep 2. In an essay on the methods used in the study of sleep. Total sleep deprivation Humans These studies tend to be carried out on student participants at various universities, for example Loughborough and Edinburgh in the UK. There are also the two infamous cases of sleep deprivation for the purposes of charity and notoriety in the Guinness book of records. Case studies Peter Tripp stayed awake for a ‘wakeathon’ charity event for 8 nights. He reported hallucinations such as seeing his desk drawer on fire and delusions.
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