Sleep

Circadian rhythms last for about 24 hours. 

The sleep-wake cycle:

• External cues e.g. darkness & the time on a clock tell us when to go to sleep
• Free-running cycle maintains the sleep-wake cycle in the absence of external cues. It is governed by an internal (endogenous) clock. 
• Cycle can be entrained (i.e. brought into phase) to some extent by external cues.

Core body temperature

• Body temperature is generally lowest at 4:30am & highest at 6:00pm
• Post-lunch dip - tiredness in the afternoon may appear to be due to the effects of having eaten, but it occurs even if you don't eat - due to a circadian temperature rhythm.

Hormones

• Cortisol levels are lowest at midnight and peak at about 6am. When levels are high, this creates alertness - which explains why you can't think clearly when you wake up earlier than normal (your cortisol levels are lowe and therefore you aren't alert)
• Melatonin & growth hormone levels peak at midnight

• Supported by temporal isolation studies that demonstrate the free-running circadian rhym, & show that the cycle persists despite the absence of light, for example: Siffre spent long periods of time underground with no daylight, radio, etc. He found that his sleep-wake cycle generally adjusted to a 24-hour cycle (but sometimes changed dramatically to as much as 48 hours) 
• There are individual differences: cycle length varies from 13 to 65 hours (Czeisler et al) and cycle onset varies, there are innate patterns of waking & sleeping: morning types (rise at 6am & go to bed at 10pm) and evening types (rise at 10am & go to bed at 1am) - Duffy et al
• Case studies lack validity - Siffre's findings were based on one unique individual, so lacks generalisability. However, they have been confirmed by other studies. On the plus side, he also used an experimental approach, and therefore could demonstrate a causual relationship between external cues & sleep-wake cycle
• Cycle can be entrained is supported by Folkard et al - they gradually reduced participants' circadian rhythm using a quickening clock, but when the 'day' was reduced to 22 hours, the participants' own rhythms took over again, showing a limit for control of interla rhythms by external cues.

• Variation in body temperature explains superior recall & comprehension in 12-13 yr olds working in the afternoon rather than the morning (Folkard et al)
• Cause or correlation? Giesbrecht et al diliberately lowered core body temp & showed that this caused lower cognitive performance. It is not clear whether the effect is due to the direct effects of core body temp, or whether the high core body temp leads to increased physiological arousal & this creates the effect. However, Hord & Thompson found no link between body temp & cognitive performance
• IDA - A biological & determinist approach - All of these explanations suggest that our sleep-wake patterns are fixed, caused by internal mechanisms and/or external cues. The study by Folkard et al shows that there is some flexibility in the system. One person in his study did manage to keep a 22-hour rhythm, which shows that other factors can override the internal clock

Ultradian rhythms occur more than once in a day

Desecending the sleep staircase

• Stages 1 & 2 - relaxed, alpha & theta waves, heart rate slows, temperature drops
• Stages 3 & 4 - called deep sleep (or slow wave sleep, SWS), delta waves, metabolic rate slows, growth hormone produced
• REM sleep (rapid eye movement) - associated with dreaming, desynchronised EEG activity similar to the awake brain, brain & eyes active but body paralysed.
• One cycle takes about 90 minutes; later in the night there is more REM sleep & less SWS. 

Basic rest-activity cycle

• During the daytime there is also a 90-minute cycle of rest followed by activity. Friedman & Fisher observed psychiatric patients over a 6-hour period, & noted a clear pattern of 90 minutes between eating & drinking 'episodes'. 

• There are age differences - babies don't have the same stages; they display quiet & active sleep, which are immature versions of SWS & REM sleep. Relatively greater amounts of REM sleep may be related to the considerable learning that is taking place. Older people experience reduced SWS & an associated reduction in the production of growth hormone. This may explain some of the symptoms associated with old age e.g. lower bone density
• The link between REM sleep & dreams has been questioned - Dement & Kleitman demonstrated that people awoken during REM sleep were often dreaming, but dreams are not exclusive to REM sleep, often occuring at other times as well. 
• The value of the 90-minute rhythm - ensures that biological processes in the body work in unison. Complex metabolic processes are active in many different parts of the body at any time & some coordination between these is advantageous. 

Monthly cycles

• Menstrual cycle is determined by fluctuating levels of female hormones that regulate ovulation. The pituitary gland releases hormonse (FSH & LH), egg ripens & triggers the production of oestrogen & later progesterone to prepare the lining of the womb for a fertilised egg. If there is no pregnancy, progesterone levels fall and the lining is shed. 
• Males also have been found to have near-monthly rhythms for temperature & alterness levels. 

Seasonal affective disorder (SAD)

• A yearly cycle - people with SAD are depressed in winter & recover in summer. This may be due to the hormones melatonin & serotonin - more darkness means more melatonin & more melatonin means less serotonin. Low levels of serotonin are associated with depression.

• Can be controlled exogenously - Russel et al showed that pheromones can entrain menstrual cycles (by collecting sweat from one group of women & rubbing it on the upper lips of another group of women). This shows that biological rhythms can be entrained by exogenous cues. 
• May have negative effects - Premenstrual syndrome (PMS) is associated with certain direct effects: anxiety, depression, mood swings & aggression. Such behaviours were once considered 'all in the mind' but now there is a recognised biological cause. 
• IDA - A determinist approach - Both SAD & PMS suggest that certain behaviours are inevitable - & this has been used as a legal defence e.g. Ms English was placed on probation (rather than a custodial sentence) for the murder of her boyfriend because she was suffering from severe PMS.
• Could be explained differently - SAD might not be an effect of infradian rhythms, but due to a disrupted circadian rhythms, similar to jet lag - happens because we go to bed earlier as it's darker eaarlier in winter & this puts rhythms out of phase. 
• IDA - Real life application - Phototherapy developed to treat SAD by exposing sufferers to very strong light. However, benefits of phototherapy may be due to a placebo effect as, in one study, 32% improved with a placebo alone. 

The Syprachiasmatic Nucleus (SCN)

• The SCN is a cluster of nerve cells in the hypothalamus. It receives information about light because it is located above the optic chiasma. Even when the eyes are shut, information about light is received by the SCN.
• One SCN is in each hemisphere, each divided into: ventral SCN, relatively quickly reset by external cues and dorsal SCN, less affected by light.

The Pineal Gland & Melatonin

• The pineal gland recieves signals from SCN, and as a result produces melatonin. 
• Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness.

• The effect of the SCN has been demonstrated - In animal studies, e.g. Morgan bred 'mutant' hamsters with 20-hour circadian rhythms. When their SCN was transplanted into the 'normal' hamsters they exhibited the mutant rhythm. 
• IDA - An issue is the use of non-human animals - Animals used in this research are permantely harmed, which can be justified if the research is regarded as important e.g. it can be argued that it is important for understanding the effects of desynchronised biological clocks in shift workers & providing suggestions for how this might be overcome. However, generalisations made from animal to human behaviour may not be justified as biological systems are different, & also humans have the power of cognitive control over their behaviour, at least in some situations.
• IDA - The evolutionary approach can help us understand the adaptive nature of biological rhythms e.g. anticipanting daily environmental events. Chipmunks without functioning SCNs were found to be more likely to die, presumably because they were awake at night & making noise, which attracted predators (DeCoursey et al)

Light

• Light entrains the free-running biological rhythm - This affects the SCN & other peripheral oscillators, e.g. Campbell & Murphy shone light on the back of participants' knees & reset circadian rhythms. 

Social Cues

• Social coventions entrain biological rhythms - e.g. mealtimes reset cells in the heart & liver

Temperature

• Cold temperature - signals a time for reduced activity
• Warm temperature - is the time for activity (sleep-wake). In warm-blooded animals, daily changes in body temperature are governed by their circadian clock & these temperature changes entrain other circadian rhythms (Buhr et al)

• One issue is whether artificial lighting is enough - Early studies of biological rhythms exposed participants to artificial lighting & it was assumed this would not be bright enough to entrain rhythms (e.g. Siffre cave study). However, Campbell & Murphy shifted rhythms with light on the back of knees. Boivin et al found that even artificial lighting does have an effect, although bright lighting is better for resetting circadian rhythms. 
• IDA - Real world application - Living in an artificially lit world may disrupt melatonin production, so leading to increased incidence of cancer
• There are advantages with this blended system - endogenous & exogenous cues act as one system. Total isolation studies are artificial; in the real world both cues interact to enable internal synchronisation of physiological processes, but also external synchronisation with enevitable environmental changes.

Organisations & industries that work around the clock require their employees to do shift work. This means that employees are required to work when they would normally sleep & to sleep when they would normally be awake. 

A classic pattern is to divide the day into 3 eight-hour shifts: Midnight to 8am, 8am to 4pm and 4pm to midnight.

Switching shifts obviously disrupts links between external zeitgebers and therefore biological rhythms need some time for readjustment.

• Alertness decreases when cortisol levels are lower in the middle of the night, when core body temperature is also lowest (circadian trough)
• Sleep deprivation is inevitable because sleeping during the day is disrupted by noises & daylight; sleep length is typically 2 hours less than normal.
• Effects on health e.g. shift workers are three times more likely to develop heart disease.

• IDA - Real world application - Our society relies on shift work & therefore it is essential to understand & reduce the negative effects caused by working shifts. Many major disasters can be blamed on errors arising from the disruption of biological rhythms that are associated with shift work.
• An alternative explanation - Shift work effects are not just due to the direct effects of disruuption of rhythms, but indirectly to such things such as the associated social deprivation & family disruption, e.g. divorce rates may be as high as 60% in shift workers (Soloman)
• IDA - Real world application - Research has found systems that have fewer negative effects. Non fluctuating shifts are better, i.e. a week of working days, followed by a week of working nights. Forward-rotating shifts (phase delay) are better than backward-rotating shifts
• IDA - Real world application - Artificial lighting can be used to entrain circadian rhythms & promote wakefulness. Boivin et al showed that very bright lighting can reset the biological clock. They found that, within three days, a group of participants exposed to a very bright light had advanced their biological clock by 5 hours, wheras exposure to an ordinary light advanced participants by 1 hour & dim lighting led to a 1 hour delay.
• Lab experiments should be verified - Lab experiments demonstrate causal relationships but should be confirmed by more natural studies. 

'Jet Lag' describes the pysiological effects of desynchronised circadian rhythms. Symptoms include nausea, fatigue, disorientation, insomnia & depression. It is estimated that the dorsal part of the SCN takes several cycles to adjust to large ennvironmental changes.

Phase delay is easier to adjust to - the same as staying up later than usual or travelling east to west.

Phase advance is more difficult because you wake up when you're in a circadian trough - same as getting up earlier or travelling west to east. 

For example, US baseball results were better for teams travelling east to west - they won 44% of their games over a three-year period compared to 37% wins for teams travelling west to east (Recht et al). This suggests that the east to west teams suffered less from jet lag than the west to east teams.

• An alternative explanation - The effects of jet lag may be due to other factors related to travel, such as long hours of travel, annoyance caused by other passengers and low oxygen cabin air
• IDA - Real world application - Melatonin may reduce the effects of jet lag because it naturally induces sleep. Herxheimer & Petrie reviewed 10 studies & found melatonin was very effective if taken just before bedtime, but when taken at other times of the day it may delay adaptation to local time. 
• IDA - Real world application - Social cues entrain biological rhythms, so one way to cope with jet lag is to eat & sleep at the right times. Fuller et al found that a period of fasting followed by eating at the right time helps to entrain biological rhythms. 
• It is important to consider individual differences - Some people are more affected by circadian disruption than other - Reinburg et al found that people whose circadian rhythms adapt more slowl actually cope best with shift work/jet leg. 

Infancy

• Duration - Babies sleep for about 16 hours a day, but not continuously. They wake every hour or so cycles less than an adult 90-minute cycle). 
• Patterns of sleep - Active & quiet sleep - version of REM sleep & SWS. About half of infant sleep is 'active' - more than adult ration of REM:NREM. Infants don't go immediately into SWS; they start with very light sleep & are therefore easily awoken.
• Circadian rhythm - By about 6 months most children have one main sleep-wake cycle, with a few naps during the day. 

• IDA - A developmental approach - The lifespan approach is important because it recognised that sleep patterns are not consistent but change as we age. This has led to new understanding of, for example, some of the effects of ageing. 
• IDA - An evolotionary approach - Suggests that infant sleep patterns evolved so that parents can get on with daytime chores. Infant sleep patterns evolved because infants have small stomachs & must wake & eat regularly. 
• There is a reason why infants have large amounts of active sleep - Active REM sleep is associated with the production of neurotransmitters & consolidation of memory - both apply to infant development. This is supported by research that shows that premature babies (whose brains are even less mature) spend 90% of sleep time in active sleep. 

• Children typically sleep about 12 hours a day, and EEG patterns resemble adult patterns. The amount of sleep gradually decreases.
• Parasomnias common in childhood, such as sleep walking & night terrors. 

• IDA - Cultural bias - Psychologists make assumptions about sleep behaviour based on research with American and British samples. Tynjala et al found considerable differences in sleep patterns across European countries in children of 11-12 years e.g. Israeli children sleep 9 hours on average. This shows that sleep duration is influenced by cultural practices. Our view of behaviour often ignores such influences.

• Sleep duration increases in adolescence. Boys often have org*sm & ej*culation during sleep. 
• Phase delay - Circadian rhythms shift so teenagers stay awake later and wake up later.

• Adolescent sleep can be explained by hormone changes - Adolescence is a time where there are major changes in sex hormones. These changes disrupt sleep because hormones are predominantly released at night. Many 'symptoms' of adolescence (e.g. moodiness, lack of motivation) may be due to sleep problems.
• A consequence of phase delay - Schools should adjust their school day to fit delayed sleep phase syndrome, which is typical of adolescents and means they have poor attention spans in the morning. 

• Typically 8 hours per night, 25% of which is REM sleep.
• Increasing frequency of sleep disorders such as insomnia and sleep apnoea. 

• Too much sleep is not necessarily a good thing - Kripke et al surveryed 1 million adults and found that sleeping for 6-7 hours was associated with reduced mortality, whereas an average of 8 hours had a 15% inceased risk of mortality and sleeping more than 10 hours was linked to a 30% increased risk.
• Correlational data doe mean a cause has been demonstrated - It is likely that underlying illness is an intervening variable. 

Sleep patterns change

• More difficulty going to sleep, and wake more frequently. 
• REM sleep decreases to 20% of total sleep time
• SWS decreases to 5% of total sleep time
• Phase advance; go to sleep earlier and wake up earlier.
• May nap during the day to satisfy sleep needs

• Reduced sleep is a consequence of phsysiological changes, but also problems staying asleep, e.g. insomnia and reduced SWS means people are awoken more easily
• A consequence of sleep changes is less growth hormose is produced (because less SWS), which may explain some of the symptoms of old age e.g. lack of energy and lower bone density. Lack of sleep may also explain impaired cognitive functions.
• IDA - Real world application - Sleep quality can be improved through the use of melatonin. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness. 

Slow wave sleep (SWS)

• SWS initiates body repair (Oswald)
• Growth hormone - Important in childhood because it stimulates physical growth. Important throughout lifespan for protein synthesis & cell growth (cells need to be constantly replaced). Secreted to some extent during the day but mainly in SWS. This is demonstrated by reversing the sleep-wake cycle and then growth hormone is produced during the day when SWS takes place. The amount of growth hormone correlates with the amount of SWS. 
• Immune System - Body's defence against viruses and baceria. Lack of SWS is associated with reduced immune funcioning. 

REM Sleep

• REM sleep initiates brain repair (Oswald)
• Brain growth - infants have a greater proportion of REM (i.e. active) sleep than adults, which suggests that REM sleep may be important for brain growth. Siegel suggests that the amount of REM sleep in any animal is proportional to the immaturity of offspring at birth.
• Neurotransmitter function - Siegel and Rogaski suggest that during REM sleep, neurotransmitters are not produced, allowing neurons to regain their sensitivity. Antidepressant drugs abolish REM activity - and also replenish neurotransmitters, supporting the link between REMM and neurotransmitter recovery (antidepressant drugs increase neurotransmitter levels. 
• Memory - REM sleep may permit memories to be sorted & discarded if unwanted. REM may be important in the consolidation of procedural memory (memory for doing things), whereas SWS is important for semantic & episodic memory (memory for events and meanings).

• There are methodological issues - Case studies relate to unique individuals, and other sleep studies often use volunteers who also might have unique characteristics (e.g. have less need for sleep than the norm) - so results might lack generalisability. Non-human animal studies might lack generalisabilty because animals have different sleep requirements to humans. 
• If sleep (SWS & REM) is restorative, exercise should increase the need for sleep - Exercise should use up proteins, etc, necessitating more sleep for restoration. Shapiro et al found that marathon runners slept 2 horurs longer after a race. However, Horne found that a series of exhausting tasks led people to go to sleep faster but not for longer.
• IDA - The evolotuinary approach - The main alternative to restoration theory is the evolutionary approach, which claims that sleep has no specific benefit except protection (to conserve energy or keep an animal safe from predators), rather than performing some specific biological function as claimed by the resoration approach. The restoration approach doesn't explain, for example, why some species sleep one hemisphere at a time. Nor does it explain why lack of consciousness is neccessary. It looks like environmental pressures are important in shaping sleep processes, which can be explained by the evolutionary approach. 

Energy Conservation

• High expenditure of energy - Warm-blooded animals (such as birds or mammals) use energy to maintain temperature. This is especially true for small animals with a high metabolic rate (such as mice).
• Benefits of sleep - Sleep provides a period of enforced inacitvity to conserve energy, such as hibernation (Webb called it the hibernation theory of sleep). Therefore small animals should sleep lots to conserve energy. 

Foraging Requirements

• Time spent asleep (conserving energy) - is constrained by time needed for eating. Herbivores have to spend a lot of time eating becaue their food is poor in nutrients. Carnivores can afford to sleep a great deal. 

Predator avoidance

• Time spent asleep (conserving energy) is contrained by risk of predation. Predators can sleep for longer. Prey species are in danger when sleeping. However, if sleep is vital, then it is best to be done when the animal is least vulnerable i.e. at night when they can hide.

Waste of Time

• Sleep is wasting time - Meddis proposed that sleep is what animals do when they have nothing else to do with their time. For most animals, this means sleeping at ngith & sleeping out of sight (in a burrow) because they are not as vulnerable while they are asleep.
• Being awake is dangerous - Siegel also pointed out that being awake is dangerous, not just because of predation, but also because an animal is more likely to be injured.
• The best adaptive strategy is to sleep as long as you can. 

• Predicts a negative correlation between body size & sleep. Supported by Zepelin & Rechtschaffen, who found smaller animals sleep more than larger anials, although there are exceptions e.g. sloths who are large & sleep a lot. However, not supported by Capellini et al who found a positive correlation. This study used carefully selected, standardised data & therefore may be more reliable than older evidence. 
• Energy is only conserved in REM sleep - In REM sleep the brain is relatively active so energy may actually only be conserved in NREM sleep. This suggests that only NREM sleep evolved for energy conservation. More primitive animals (e.g. reptiles) only have NREM sleep, supporting the view that NREM sleep evolved first (for energy conservation) and REM sleep later (to maintain brain activity). If this is correct we would expect a negative correlation only between body size & NREM sleep. Supported by Allison & Cicchetti but not by Capellini et al. 
• Predicts a trade-off betwen foraging needs & sleep - Capellini et al found that animals with a greater need for foraging (because of high metabolism or diet low in energy) had lower sleep rates, supporting foraging needs as an explanation for sleep patterns. 

• Predicts a trade-off between predation risk & sleep - Alison & Cicchetti found that species with a high risk of predation did sleep less. Though there are exceptions, e.g. rabbits (high risk of predation) slept as much as moles (low risk of predation). However, Capellini et al found the relationship is complex e.g. animals that sleep socially sleep fewer hours - but ought to sleep more because is safety in numbers.
• IDA - The Evolutionary Approach suggests that sleep must be adaptive in some way, otherwise why do all animals do it it, but their patterns of sleep differ? This suggests that these patterns are in some way adaptive to the species' environment. 
• IDA - The Restoration Approach suggests that sleep evolved not just to occupy wasted hours, but because vital functions are performed. Horne proposed a way to combin both approaches: Core sleep (=SWS), essential for bodily restoration & Option sleep (=REM and some NREM sleep), dispensable but useful for occupying unproductive hours.

Short-term insomnia - Insomnia lasting a few weeks tends to be caused by immediate worries e.g. exams or recent death in the family

Long-term insomnia - Lasting more than 4 weeks (a DSM definition). Long-term insomnia is divided into primary & secondary insomnia.

Difficulties sleeping that are not directly associated with any other health condition or physical cause (such as drug abuse or medications). 

May be due to:

• bad sleeping habits e.g. drinking coffee in the evening, having naps during the day.
• Expectations of sleeping problems because of a previous cause e.g. depression. The original problem has disappeared but there is still an expectation of sleep problems, which act a self-fulfilling prophecy leading to continuing sleep problems. 

Dement; half of all humans acknowledge that they have difficulty sleeping & only 5-10% of sufferers get diagnosed. He believes that insomnia is not a sleep disorder but is a symptom that can have many causes.

• Psychophysiological insomnia: an anxiety-induced insomnia, learned behaviour, may fall asleep when they don't intend to e.g. whilst watching TV. Treatments: CBT, change faulty thoughts, improve sleep habits & sleep hygiene. 
• Idiopathic insomnia: could some people be 'wired' for insomnia? There is a possibility of damage to the SCN. This leads to the brains loss of control to the sleep-wake cycle. Treatments: drug therapy.
• Sleep state misperception: when asked about sleep, these people underestimate their total sleep time and over-estimate the time it took them to sleep. 

Sleep difficulty is a symptom of something else i.e. insomnia is secondary to this other condition, such as:

• Hormonal changes (particularly in women)
• Decreased melatonin production (Age 60+ produce very little melatonin)
• Medical conditions (e.g. high blood pressure, CHD, Parkinson's disease)
• Psychiatric conditions (e.g. post-traumatic stress, anxiety, depression, etc.)

Treatments

It is important to treat the underlying problem that is causing insomnia

• CBT
• Supplements
• Drug Therapy

• IDA - Real world application - The distinction between primary & secondary insomnia is important when deciding on treament, because either you should treat the insomnia (if it is primary insomnia) or you should treat the underlying cause (in the case of secondary insomnia). For example, in the case of insomnia arising from depression it might be unhelpful to treat only the insomnia. However, it is not always clear whether insomnia is simply a symptom of the main cause (i.e. secondary) or in fact primary. 
• Insomnia is studied because it has important consequences: Cognitive impairment - Zammit et al found that patients experiences problems with concentration, memory & problem solving. Accidents - The National Traffic Safety Administration estimates that 15,000 deaths annually aer related to sleepiness/fatigue. The effects of tiredness have also been linked to industrial accidents as a result of shift work. Psychological disturbance - Breslau et al found that insomnia was also associated with increased risks for drug & alcohol abuse. Immune system underfunctioning - Savard et al found fewer immune cells in the bodies of people with chronic insomnia compared with good sleepers. This would make insomniacs more vulnerable to physical illness. 

• Not a sleep disorder at all - Dement states that insomnia is not a sleep disorder at all, but a symptom that occurs as a result of numerous causes. Dement accepts that many people do regard it as a disorder in itself simply becauese it is easier to talk about it in this way, but that it should always be dealt with as a symptom, and doctors should search for the cause of the symptom.
• Research complications - The large number of factors that may contribute to a person's insomnia makes it very difficult to conduct meaningful research - having so many factors leads to only small overall effects. This means that research is unlikely to uncover clear solutions to the problem. 
• IDA - Real world application - The Cognitive Approach - Attribution theory is an example of the cognitive approach. It concerns the way we think about the causes of our own/other people's behaviour. In the case of insomnia, if a person believes they cannot sleep because of insomnia this produces self-fulfilling expectations i.e. they don't sleep as a result. Attribution therapy suggests than an individual needs to think differently about the causes of their behaviour i.e. learn to make a different attribution about why they are not sleeping. Storms & Nisbett tried this with insomniacs. They gave the insomniacs a pill & told them it would either stimulate them or make them sleepy. Those who expected the pill to stimulate them went to sleep faster because they attributed their usual bedtime arousal to the pill & therefore relaxed more.

Repeated episodes of breathing failure during sleep. Features: snoring, morning headache

Research

Peever - repeated distruption of normal lung activity triggers a form of learning that helps you breathe better. This type of brain plasticity could be harnessed to help overcome the breathing insufficiency that typifies sleep apnoea.

Treatments

• Surgery - widen airways
• Weight loss
• Breathing mask - continuous airway pressure
• Drugs - to help the underlying condition of heart failure

Symptoms of sleep paralysis, cataplexy, hypnagogic hallucinations & daytime sleepiness.

• Psychological explanations - Lehrman & Weiss suggested that sudden attacks of sleepiness disguise s*xual fantasies. 
• Biological explanations (malfunction of REM system) - Makes sense because classic symptoms of narcolepsy match REM sleep characteristics, for example: paralysis (lack of muscle tone) and intrusion of REM-type sleep (hallucinations) into daytime. Therefore narcolepsy may be related to malfunction in system that regulates REM. 
• Mutation in hypocretin - The neurotransmitter hypocretin plays a role in keeping people awake. Hypocretin is produced by cells in the hypothalamus. In narcoleptics a large number of these hypocretin cells are missing, resulting in lowe levels of hypocretin.

• Little research support - psychological explanations have had little support & are now not generally included when considering the causes of narcolepsy.
• There is some research support for the malfunction of REM - Vogel observed sleep patterns during narcoleptic episodes in one patient, and found (as predicted) that REM patterns were present at the beginning of each episode. However, generally there is little research support for the REM malfunction explanation.
• There is research support for the role of hypocretins - Lin et al found that narcoleptic dogs had a mutation in a gene on chromosome 12, which affects hypocretin production. Findings from dogs confirmed in humans e.g. narcoleptics had lower levels of hypocretin. However, hypocretin loss in humans is not linked to inherited factors because narcolepsy doesn't run in families & not concurrent in MZ twins. Low levels of hypocretin is likely to be due to brain injury, diet stress or auto-immune attack (body's immune system turn on itself). 
• IDA - Real World Application - The role of hypocretins may lead to a treatment for narcolepsy, although it would need to be an artificial drug as the hypocretin molecule is unstable (is broken down before it reaches the brain). Alternatively it may be possible to transplant normal hypocretin cells.

• Due to incomplete arousal - Sleep walking is a disorder of arousal, the sleep walker is asleep but engaged in taks normally associated with being awake. EEG recordings during sleep walking show delta waves (typical of SWS) plus beta waves (typical of awake state). Person in SWS is awakened but arousal is incomplete.
• Risk factors - Sleep walking increase by sleep deprivation, having a fever, stress, alcohol & psychiatric conditions. Hormonal changes in puberty & menstruation may also be triggers but possibly only for genetically vulnerable individuals. 
• Why children? Possibly because children have more SWS or because the system that usually inhibits motor activity in SWS isn't fully developed in chldren (and may be underdeveloped in some adults) One study did find that adult sleep walkers showed signs of immaturity in the relevant neural circuits.

• IDA - Nature & Nurture - Genetics & Environment - The evidence for a genetic basis for sleep walking: Prevalance of sleep walking in first degree relatives is 10 times greater than in the general population. There is a 50% concordance rate for sleep walking in MZ twins compared with only 15% in DZ twins. A gene has been identified for sleep walking.  The environmental component acts as a 'stressor' as in the diathesis-stress model, for example: sleep deprivation led to an increase in sleep walking in vulnerable individuals (i.e. those who had past experiences of sleep walking). Levels of sleep walking rose from 50% to 90% after 25 hours' of sleep deprivation. Children have higher levels of SWS which acts as a diathesis.
• IDA - Real World Application - Sleep walking is occasionally used as grounds for a defence in murder trials.