APNEA
Sleep apnea is a breathing disorder during sleep, usually accompanied by loud snoring. It consists of brief periods when breathing stops. Obstructive sleep apnea, the most common type, is due to an obstruction in the throat during sleep. This can be caused by a number of factors, including obesity or other physical characteristics. Central sleep apnea, which is much rarer, is caused by a malfunction in signals from the brain governing breathing. Both forms mean that the sufferer must wake up briefly in order to breathe, sometimes hundreds of times during the night. Usually there is no memory of these brief awakenings, but in severe cases it can result in extreme sleep deprivation and death.

BEDWETTING (ENURESIS)
Approximately 15 per cent of children wet the bed after the age of three, and although it usually stops by puberty it can continue into the teenage years. It affects more boys than girls and may run in families. Only rarely does bedwetting signify a kidney, bladder or other physical problem. Nor, although emotional disturbance is often the cause, is this invariably so. Advice should be sought from the family doctor if necessary, but the most important thing is to provide reassurance and emotional security to the child, and to make it clear that there is nothing to be ashamed or worried about and that s/he will be able to remain dry at night in time.

THE BRAIN
Different areas of the brain specialise in different kinds of thinking. Identifying which areas are active during sleep may help to uncover some of the mysteries of dreams and their purpose. During non-REM sleep, there is very little brain activity, but during the REM interludes a frenzy of electrical impulses may be observed. However, the most evolutionarily advanced and sophisticated areas of the brain -- the most frontal areas -- remain inactive. When these are not working, it makes thinking disjointed, strange, illogical and disorganised -- as in dreams. Instead, the main activity during REM sleep takes place in the more primitive region of the brain, the limbic system, which is concerned especially with emotion and motivation.

BRAINWAVES AND SLEEP
Electroencephalogram (EEG) readings of electrical activity in the brain have identified four principal types of brainwaves: beta, alpha, theta and delta waves. Beta waves are associated with an alert and excited state of consciousness and alpha waves with a relaxed state. Theta and delta waves are associated with brain activity during sleep. (See STAGES OF SLEEP.) In Stage 1 of sleep, mainly theta activity, with some alpha waves, is observed. In Stages 2 and 3, there is mainly theta activity, with occasional delta waves in Stage 3. And in the deep sleep Stage 4, the predominant brain activity involves delta waves.

CIRCADIAN RHYTHMS
Both humans and animals have an innate "circadian" daily rhythm. Oddly, this follows a 25-hour cycle, and is reset each day in response to environmental clues. There appear to be two natural "sleep gates" during this cycle -- one in the early afternoon and one between around 11pm and 5am. If these "gates" are missed, it may be very difficult to get to sleep at other times, even when very tired. This is at the root of sleep difficulties associated with shift work and jet lag. Similarly, a series of late nights can also disrupt the body's natural rhythms, making sleep difficult. The body seems to be readily able to lengthen its daily cycle to accommodate one or more late nights, but to have great difficulty in shortening it, no matter how sleepy an individual may be. So, even a single late night can have the effect of shifting the circadian cycle forwards, together with the relevant "sleep gates". This means that attempting to revert to an earlier bedtime after a series of late nights can result in an individual being unable to sleep despite being extremely tired. A "delayed sleep phase syndrome" develops, involving a pattern of sleeplessness at night, problems in getting up in the morning and daytime tiredness.

COT DEATH (SUDDEN INFANT DEATH SYNDROME)
Sudden Infant Death Syndrome (SIDS) refers to the unexplained death of an apparently healthy child, usually in the first two to six months after birth. The death occurs during sleep without any apparent pain or suffering. SIDS is one of the most common killers of young infants in the developed world, but it has so defied all attempts to either predict or prevent it -- except that public health campaigns encouraging parents to sleep an infant on its back rather than its front appears to have dramatically reduced SIDS fatalities in some countries. Strangely, the majority of deaths occur in winter, male infants are more susceptible than females and a second child is more often a victim than a first. Research has also suggested some correlation with risk factors such as maternal smoking and hard drug use, poor prenatal care, low birth weight and young maternal age. With the probable exception of smoking, however, the evidence is inconclusive.

DAYDREAMS
Research has found that depriving people of REM sleep has resulted in the subjects starting to dream during the day. It seems that the urge to dream is so powerful that the brain seeks to compensate for any loss by dreaming while awake. This is confirmed by the fact that at end of sleep deprivation experiments, the subjects take greatly increased amounts of REM sleep, both in absolute terms and as a proportion of their total sleep.

DINOSAURS AND THE DUCK-BILLED PLATYPUS
REM sleep is found in all mammals. For example, the duck-billed platypus, the most primitive of egg-laying mammals, experiences six times the amount of REM sleep as humans. The species co-existed with the late dinosaurs, so is it possible that they too had REM sleep and dreams?

DREAM LABORATORY
Researchers at the "dream laboratory" at the Moses Maimonides Medical Centre, State University of New York, have investigated the possibility of the existence of precognitive or telepathic dreams. One of the largest ever experiments in the field in 1971 involved the Grateful Dead rock group projecting randomly-chosen images on a giant screen at concerts held on six successive evenings. The audience at each concert was asked to try to "transmit" the images to an English psychic while he slept at the laboratory. The research team reported that on four of the six occasions his dreams bore marked similarities to the projected images.

DREAM TIME
Many societies have based a large part of their culture around dreams and dreaming. The Aborigines of Australia have a concept known as Dream Time. This represents both a former "golden age" when the land and its aboriginal people were first created and a state of being in the present. This can be entered or experienced through dreams or a dreamlike state in which the dreamer embarks upon a symbolic mental journey.

EMOTIONAL REGULATION/PROCESSING
The paralysis associated with REM sleep makes all species that experience it very vulnerable in that state. This suggests that it must convey significant benefits for natural selection to have favoured it in the course of evolution. The association of REM sleep disorders with emotional behaviour (see, for instance, narcolepsy, which is triggered by strong emotions) suggests that REM sleep performs some kind of emotional regulation or processing function. Among the most favoured current theories is the notion that the unconscious brain is engaged in a kind of problem-solving activity during the various phases of REM sleep, sorting through various emotional memories and responses in an attempt to deal with issues that weigh on the conscious mind. See also BRAIN.

FATAL FAMILIAL INSOMNIA
Just after his 40th birthday in 1991, Michael Corke, a Chicago music teacher, began to have problems with sleeping. Over the next few weeks the problem got worse and worse, and as the sleep deprivation took its toll his health began to deteriorate. Doctors were baffled as to the cause until eventually fatal familial insomnia, an extremely rare genetic disorder discovered seven years earlier, was identified as the culprit. The disorder, which involves damage to the sleep trigger in the brain, has no known cure. After six months without sleep, Michael Corke died. Twenty five families are known to carry the gene worldwide; it will kill all those who have it.

HEARING IN SLEEP
Our sense of hearing is never switched off. This means that anything we can hear while awake will still be audible to us in sleep. As well as explaining why we can be woken from even the deepest sleep by sudden or unfamiliar noises, this also means that sounds and other sensory stimuli can be incorporated into our dreams.

INSOMNIA
Around one third of the population is likely to suffer from insomnia at one time or another. For most people this will be temporary and present no lasting problems. For chronic insomniacs, however, lack of sleep can have a devastating effect on their lives. Even relatively short periods of sleep deprivation have been shown to result in disorientation, dizziness, impaired concentration, lack of motivation, irritability, hand tremors and hallucinations. Serious mental and physical problems, and ultimately death, can result from long-term deprivation.

KUBLA KHAN
The poet Coleridge said that his famous poem came to him in its entirety in an opium dream, and he wrote down as soon as he awoke. Unfortunately, he was disturbed by a caller before he had finished and the rest of the poem disappeared from his memory, so that all he was left with was a fragment of what might have been a much longer masterpiece.

MYOCLONIC JERK
The common experience of suddenly being jolted from sleep to a waking state is known as a myoclonic jerk. It is caused by contractions in the large muscle groups and usually occurs in the first stage of sleep. The cause is uncertain but it may be related to the brain interpreting the slowing of breathing and the heart rate as akin to the body dying, so it sends an electrical impulse to the major muscle groups to revive them.

NARCOLEPSY
Narcolepsy is a chronic brain disorder, which involves the sudden intrusion of REM sleep into the waking state. These "sleep attacks", which can affect sufferers several times in the same day, may last for anything from 30 seconds to 30 minutes. The paralysis associated with REM sleep also breaks through, so that one of the main symptoms of narcolepsy is cataplexy -- the sudden, temporary loss of all muscle control. This produces a typical "rag doll" effect, described as being "just like a puppet with the strings cut" by one sufferer. The attacks are usually triggered by a sharp burst of emotion -- anger, laughter, pain, pleasure -- and often give rise to hallucinations and problems in distinguishing between dream images and reality. Since few doctors are trained to recognise narcolepsy, this means that it is frequently misdiagnosed as schizophrenia or other psychological disorders. The latest estimates from the US suggest that it affects 0.03% of the population. It is hereditary and affects animals as well as humans, so researchers at the Research Centre for Narcolepsy at Stanford University have been able to breed a colony of narcoleptic dogs to help in their search for a cure. The connection with emotions underlined by their research (attacks in dogs can be brought on by sensory stimulation and arousal) could give clues about how REM sleep and dreams work normally too.

NIGHTMARES
Although commonly used now to describe any alarming or frightening dream, the original use of the term nightmare referred to a crushing sensation in sleep as if something heavy was sitting on one's chest. It was formerly thought that it was an actual demon that did this -- the night mare, also known as the night hag or incubus, an evil spirit which was thought in medieval times to force itself upon women while they slept.

NIGHT TERRORS
Night terrors (also known as pavor nocturnus, incubus and severe autonomic discharge) are not the same as nightmares. While nightmares occur during REM sleep, night terrors take place occur during deep non-REM sleep -- usually within the first hour of sleep. A terror typically lasts for between five and 15 minutes, and unlike many nightmares usually leaves the subject with no recollection other than a vague sense of fear. Unlike nightmares, sufferers are not paralysed when they occur, so they may move around and possibly injure themselves. As with narcolepsy, night terrors appear to be hereditary.

OUT OF THE BODY EXPERIENCES (OBEs)
Out of the body experiences (OBEs) during sleep are surprisingly common, affecting as many as one person in ten, according to surveys. They may range from a vague sensation of travelling outside or hovering above the body to very vivid remembered dreams in which information appears to have been obtained that would not otherwise have been available to the person concerned. Not all OBEs occur spontaneously: some people have developed techniques whereby they can induce the experience at will.

PARASOMNIA
Parasomnia is a term used to describe sleep disorders that occur usually in non-REM sleep. Parasomnias include night terrors, bed wetting (nocturnal enuresis), sleepwalking and sleep talking.

PERIODIC LIMB MOVEMENT SYNDROME (PLMS)
Uncomfortable prickling sensations and involuntary twitching of the legs, most commonly in the first stage of sleep, is known as PLMS. It can usually be treated with medication.

REM SLEEP
REM, or Rapid Eye Movement sleep, was first reported by the physiologists Eugene Aserinsky and Nathaniel Kleitman in 1953. It refers to the rapid, jerky movements of the eyes which characterises periods of frenzied brainwave activity during sleep. These REM sleep phases occur at regular 70-90 minute intervals, and their observation put an end to the previously-held notion of sleep as a uniform deactivation of the central nervous system to allow the body to recuperate. REM sleep is associated with dreaming, as a result of which it is accompanied by the suppression of muscle control. This protects against harm being done to the body by trying to act out movements or potentially dangerous activities occuring in the dreams. Adults spend about a quarter of their time asleep in REM sleep, compared with more than half in babies. The human foetus appears to spend the great bulk of its time in REM sleep, although there is no muscular paralysis at this stage. This accounts for the familiar twitching and kicking of the foetus in the womb, which represent involuntary movements during REM sleep.

SLEEPING PILLS
"Sleeping pills" are often used in the treatment of insomnia. There are two main varieties: barbiturates and tranquilisers. Of the two, barbiturates have been found to be less effective; they are also extremely addictive. Side effects can include depression and loss of muscle control. In common with both caffeine and alcohol and a range of othrer drugs, it suppresses REM sleep. Tranquilisers are effective in the short-term relief of insomnia, but work less well if used for more than two weeks at a time. Longer-term use can also result in addiction. In recent years, melatonin, a natural hormone secreted at night by the pineal gland, has been advocated as a "natural" remedy for insomnia. Pills currently sold over the counter, however, may contain up to the ten times the very small dose that has been found to be most effective. Larger doses can result in a melatonin "hangover" and drowsiness the next day.

SLEEP PARALYSIS
Paralysis of all the major muscle groups except those governing the heart and breathing is a normal feature of REM sleep. Its function is to prevent the body from harming itself by acting out dreamed actions. The paralysis can sometimes continue temporarily after waking up (sometimes known as "old hag"), but this usually lasts for only a few seconds.

SLEEPWALKING
Sleepwalking is a term used to describe a variety of unconscious actions, not just walking, carried out by someone during deep sleep. It occurs most often among children before they reach puberty, but does affect adults too. It is potentially extremely dangerous because, in effect, the sleepwalker is acting out a dream. If that dream appears threatening, the sleepwalker may become violent, thinking himself under attack.

SOMMATIC DREAMS
Dreams which anticipate illness in the body are known as sommatic dreams. There have been a number of documented cases of people dreaming about ailments before they are aware that they have them. In one case, a mother dreamt she put her foetus in the freezer just before she had a stillborn child; in another, a woman had a recurring nightmare about wolves gnawing at her stomach -- she was subsequently diagnosed as having stomach cancer. It may be that during sleep the brain is more able to get in touch with the underlying physiology of the body, to identify possible problems and to start the process of trying to solve them through dreams. Certainly Hippocrates, the father of medicine, considered that dreams provided insights to how the body is functioning physically since he always asked his patients about theirs.

STAGES OF SLEEP
For most people, sleep follows a remarkably uniform pattern. A typical adult will require between seven and nine hours sleep a night (although there can be wide variations outside these norms). This usually consists of about five cycles of non-REM sleep broken every 70-90 minutes by interludes of REM sleep. These last from approximately five to 15 minutes at the end of the first cycle, typically increasing as sleep continues. Non-REM sleep occurs in four stages, as measured by electroencephalogram (EEG) readings of brain activity. Stage 1 is found at the onset of sleep or after being momentarily awoken; Stages 2 and 3 involve gradually deeper levels of sleep and less electrical activity in the brain; and Stage 4, which occurs after about 20 minutes, is the deepest level of sleep, at which the brain is dormant. These deeper phases of sleep are sometimes referred to as slow wave sleep because of the slow, undulating brainwave patterns they produce.

TAOISM
The Taoist master, Chuang Tzu, once had a dream that he was a butterfly, living the life of a butterfly, flying around, gathering nectar and doing all the things that butterflies do. It was such a powerful, vivid dream that when he awoke and found himself lying in his bed, he was shocked to find that he was a man and not an insect. So he asked himself, "Was I before a man who dreamt about being a butterfly, or am I now a butterfly who dreams about being a man?"

THE UNCONSCIOUS
Freud described dreams as "the royal road to the unconscious", while the followers of surrealism have described them as "volcanoes of the unconscious". Whether the interest is in psychological enlightenement or artistic inspiration, the idea of dreams as a means of tapping the unconscious mind has been prevalent throughout human history. Interest in the interpretation of these "messages" from the unconscious mind also has a particularly strong religious or spiritual streak. The Talmud says that "A dream which is not understood is like a letter which is not opened." And the Bible is full of prophetic dreams. Among the most famous is the story of Joseph's intepretation of Pharaoh's dream about seven fat cows devouring seven lean ones; this was said to refer to seven good harvests being followed by seven poor ones.

WET DREAMS
Wet dreams (often referred to as "nocturnal emissions") are dreams occuring in REM sleep which culminate in ejaculation. Although they usually occur among adolescent males who are not otherwise stimulated to orgasm, they can persist into later life and there are some reports of the female equivalent.

RESOURCES

SLEEP MATTERS
Medical Advisory Service help line, providing advice on a range of sleep disorders and details of insomnia self-help groups
0181 994 9874

BM CRYSIS
London WC1N 3XX
Helpline for parent with sleepless children
0171 404 5011

NARCOLEPSY ASSOCIATION
Tel/fax. 01273 832725