|Classification and external resources|
Sleepwalking, also known as somnambulism or noctambulism, is a sleep disorder belonging to the parasomnia family. Sleepwalkers arise from the slow wave sleep stage in a state of low consciousness and perform activities that are usually performed during a state of full consciousness. These activities can be as benign as sitting up in bed, walking to the bathroom, and cleaning, or as hazardous as cooking, driving, violent gestures, grabbing at hallucinated objects, or even homicide.
Although generally sleepwalking cases consist of simple, repeated behaviours, there are occasionally reports of people performing complex behaviours while asleep, although their legitimacy is often disputed. In 2004, sleep medicine experts in Australia claimed to have successfully treated a woman who claimed to have sex with strangers in her sleep. In December 2008, reports were published of a woman who sent semi-coherent emails while sleepwalking, including one inviting a friend around for dinner and drinks. Sleepwalkers often have little or no memory of the incident, as their consciousness has altered into a state in which it is harder to recall memories. Although their eyes are open, their expression is dim and glazed over. Sleepwalking may last as little as 30 seconds or as long as 30 minutes.
Nomenclature, classification, and codification 
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According to a study by Dr. Christina A. Gurnett, of the Washington University School of Medicine's Department of Neurology, sleepwalking may be inherited as an autosomal dominant disorder with reduced penetrance. Genome-wide multipoint parametric linkage analysis for sleepwalking revealed a maximum logarithm of the odds score of 3.44 at chromosome 20q12-q13.12 between 55.6 and 61.4 cM.
Sleep stages 
Sleep is categorized into stages of a cycle between REM sleep and NREM sleep. NREM sleep is further divided into four stages: stage 1 (a light sleep period), stage 2 (a consolidated sleep period), and stage 3 and 4 (slow wave sleep periods). This is followed by stage 3, stage 2, stage 1, and a REM period. In normal adults, a cycle will last about 1.5 hours. According to Lavie, Malhotra, and Pillar, "The length and content of sleep cycles change throughout the night as well as with age." Sleepwalking generally occurs during the first third of the night (between 11 p.m. and 1 a.m.) during the slow wave NREM sleep stage. High delta activity within the brain usually accompanies slow wave NREM sleep, and when 20–50% of all activity is delta activity, stage 3 is scored. When delta activity reaches 50% or higher, stage 4 is scored. Usually, if sleepwalking occurs at all, it will only occur once in a night.
Researchers sometimes disagree about the classification of sleepwalking as an automatism. These repetitive actions may include chewing, lip-smacking, pulling at clothing, or wandering around looking confused. Epileptic automatisms are also associated "with the absence attacks of petit mal epilepsy."
Some actions that take place during sleepwalking could be classified as "automatisms". The distinction between "non-insane automatism" and "insane automatism" may be important in the legal context (see Crime below).
Several experts theorize that the development of sleepwalking in childhood is due to a delay in maturation. There are also high-voltage delta waves in somnambulists up to 17 years of age. This presence might suggest an immaturity in the central nervous system, also a possible cause of sleepwalking. Sleepwalking is clustered in families, and the percentage of childhood sleepwalking increases to 45% if one parent was affected, and 60% if both parents were affected. However, there is no recorded preference to male or female individuals. Thus, heritable factors appear to predispose an individual to develop sleepwalking, but expression of the trait may be also influenced by environmental factors. Other precipitating factors to sleepwalking are those factors which increase the slow wave sleep stage. These most commonly include sleep deprivation, fever, and excessive tiredness. The use of some neuroleptics or hypnotics can also cause sleepwalking to occur.
There are some drugs that can be prescribed for sleepwalkers, such as a low dose of benzodiazepines, such as clonazepam, and tricyclic antidepressants. Many experts advise putting away dangerous items and locking doors and windows before sleep to reduce risks of harmful activity while sleepwalking. Good sleep hygiene and avoiding sleep deprivation is also recommended.
There are conflicting viewpoints on whether it is harmful to wake a sleepwalker. Some experts say that sleepwalkers should be gently guided back to bed without waking them. Others counter that idea and state that waking a sleepwalker may result in their disorientation, but it is not harmful.
According to the National Sleep Foundation in the U.S., sleepwalking is prevalent in 1–15% of the general populace. Sleepwalking is most prevalent in children, and usually disappears by adolescence. Sleepwalking in adults is less common, but when it does occur, the events occur three times more often per year and last for more years than in children. Sleepwalking in old age is rare and usually indicates another disorder. Old age disorders may include delirium, drug toxicity or a seizure disorder.
Sleepwalking events are common in childhood and decrease with age. According to Lavie, Malhotra and Pillar, the peak age is 4–8 years, when prevalence is 20% frequency of events.. Another report states that the peak age is eleven or twelve, with an estimated 25% of children having experienced at least one episode.  It is also known that "between 25–33% of somnambulists have nocturnal enuresis" (bed-wetting). Like sleepwalking, enuresis is more common in children and fades away as the child ages. Some children who sleepwalk are also affected by night terrors. However, night terrors are much more common in adult sleepwalkers, up to 50% more common. Some parents worry about the psychological implications of sleepwalking on their child, but Larissa Hirsch, MD, editor of the website KidsHealth, says, "Sleepwalking is not usually a sign that something is emotionally or psychologically wrong with a child. And it doesn't cause any emotional harm."
In the study "sleepwalking and sleep terrors in prepubera children" they found that if a child had another sleep disorder such as restless leg syndrome (RLS) or sleep-disorder breathing (SDB) that they had a greater chance of sleepwalking. The study found children with chronic parasomnias may often also present SDB or, to a lesser extent, RLS. Furthermore, the disappearance of the parasomnias after the treatment of the SDB or RLS periodic limb movement syndrome suggests that the latter may trigger the former. The high frequency of SDB in family members of children with parasomnia provided additional evidence that SDB may manifest as parasomnias in children. Children with parasomnias are not systematically monitored during sleep, although past studies have suggested that patients with sleep terrors or sleepwalking have an elevated level of brief EEG arousals. When children receive polysomnographies, discrete patterns (e.g., nasal flow limitation, abnormal respiratory effort, bursts of high or slow EEG frequencies) should be sought; apneas are rarely found in children. Children's respiration during sleep should be monitored with nasal cannula/pressure transducer system and/or esophageal manometry, which are more sensitive than the thermistors or thermocouples currently used in many laboratories. The clear, prompt improvement of severe parasomnia in children who are treated for SDB, as defined here, provides important evidence that subtle SDB can have substantial health-related significance. Also noteworthy is the report of familial presence of parasomnia. Studies of twin cohorts and families with sleep terror and sleepwalking suggest genetic involvement of parasomnias. RLS and SDB have been shown to have familial recurrence. RLS has been shown to have genetic involvement.
The persistence or onset of sleepwalking in adulthood is less common than in children. A 2012 study conducted by the Stanford University School of Medicine showed that the prevalence of sleepwalking adults in the United States was higher than once thought, with 3.7% of participants reporting two or more episodes per month. It is a misconception that adult sleepwalking always indicates a psychological disorder. Sleepwalking can, however, be a symptom of people with psychological disorders. In one study, adult test subjects were given the Minnesota Multiphasic Personality Inventory, a psychiatric test. According to the study, patients showed "outwardly directed behavior patterns...suggest[ing] that these adults had difficulty handling aggression. They did not support an interpretation of sleepwalking as 'hysterical dissociation'."
Psychological disorders and drug use 
In some cases, sleepwalking in adults may be a symptom of a psychological disorder or of drug use. One study, A.H.Crisp and colleagues, of St. George's Hospital Medical School in London, suggests higher levels of dissociation in adult sleepwalkers, since test subjects scored unusually high on the hysteria portion of the "Crown-Crisp Experiential Index". J.E.Orme, of the Psychology Department at Middlewood Hospital, Sheffield has suggested that "A higher incidence [of sleepwalking events] has been reported in patients with schizophrenia, hysteria and anxiety neuroses.". Also, patients with migraine headaches or Tourette Syndrome are 4–6 times more likely to sleepwalk. Some medications that may increase sleepwalking include: chlorpromazine (Thorazine), perphenazine (Trilafon), lithium, benzodiazepine (Triazolam), amitriptyline (Elavel, Endep), zolpidem (Ambien) and beta blockers.
Sleepwalking has attracted a sense of mystery, but it had not been seriously investigated and diagnosed until the last century. The 19th-century German chemist and parapsychologist Baron Karl Ludwig von Reichenbach made extensive studies of sleepwalkers and used his discoveries to formulate his theory of the Odic force.
Sleepwalking was initially thought to be a dreamer acting out a dream. For example, in one study published by the Society for Science & the Public in 1954, this was the conclusion: "Repression of hostile feelings against the father caused the patients to react by acting out in a dream world with sleepwalking, the distorted fantasies they had about all authoritarian figures, such as fathers, officers and stern superiors." This same group published an article twelve years later with a new conclusion: "Sleepwalking, contrary to most belief, apparently has little to do with dreaming. In fact, it occurs when the sleeper is enjoying his most oblivious, deepest sleep—a stage in which dreams are not usually reported." More recent research has discovered that sleepwalking is actually a disorder of NREM (non-rapid eye movement) arousal. Acting out a dream is the basis for a REM (rapid eye movement) sleep disorder called REM Behavior Disorder (or REM Sleep Behavior Disorder, RSBD). More accurate data about sleep is due to the invention of technologies such as the electroencephalogram (EEG) by Hans Berger in 1924 and BEAM by Frank Duffy in the early 1980s.
In 1907, Sigmund Freud spoke about sleepwalking to the Vienna Psychoanalytic Society (Nunberg and Federn). He believed that sleepwalking was connected to fulfilling sexual wishes and was surprised that a person could move without interrupting their dream. At that time, Freud suggested that the essence of this phenomenon was the desire to go to sleep in the same area as the individual had slept in childhood. Ten years later, he speculated about somnambulism in the article "A Metapsychological Supplement to the Theory of Dreams" (1916-17 ). In this essay, he stated to clarify and expand his hypothetical ideas on dreams. The dreams is a fragile equilibrium that is only partially successful because the repressed unconscious impulses of the unconscious system. This does not obey the wishes of the ego and maintain their countercathexis. Another reason why dreams are partially successful is because certain preconscious daytime thoughts can be resistant and these can retain a part of their cathexis as well. It is probable how unconscious impulses and day residues can come together and result in a conflict. Freud then wondered about the outcome of this wishful impulse which represents an unconscious instinctual demand and then it becomes a dream wish in the preconscious. Furthermore, Freud stated that this unconscious impulse could be expressed as mobility during sleep. This would be what is observed in somnambulism, though what actually makes it possible remains unknown.
Society and culture 
Sleepwalking has been a theme, or at least a plot device, in many dramatic works.
Literature, music, and theatre 
Dr. John William Polidori, a friend of Lord Byron's, earned his medical degree from the University of Edinburgh in 1815 with a treatise on sleepwalking. He was present at the famous gathering at the Villa Diodati on 16 June 1816 when Byron issued a challenge to him, Percy Bysshe Shelley, Mary Godwin and Claire Clairmont to write a ghost story. Polidori wrote "The Vampyre", the first vampire story in English.
Sleepwalking features in Thomas Hardy's novel Tess of the d'Urbervilles, where it is ascribed to Angel Clare's "deep distress and confusion".
The Jonathan Coe novel The House of Sleep is centred around a clinic for people with sleeping disorders including sleep walking.
Film and television 
A two-part episode of the TV sitcom, The Dick Van Dyke Show, was aired depicting Rob Petrie's shy, quiet brother Stacey (played by Jerry Van Dyke) as a sleepwalker who displays an outgoing personality when he is asleep.
In the Aaahh!!! Real Monsters episodes "Wake me when it's over" Ickis sleep walks and scares humans in his sleep after eating a chocolate rabbit.
In the Ed, Edd n Eddy episode "A Glass of warm Ed" Ed sleep walks and starts going through the cul-de-sac, breaking into the neighbors' houses and eating everyone's food.
A sleepwalking murder is the main subject of the 2009 movie In My Sleep.
In the film adaptation of Silent Hill, the protagonist's daughter suffers from sleepwalking.
In the movie Step Brothers, the main characters, Brennan and Dale, both sleepwalk.
In an episode of Gomer Pyle, USMC entitled "Gomer, Welsh Rarebit Fiend" (Season 4, episode 24) (1967), Gomer has episodes of sleepwalking caused by eating Welsh rarebit, leading Sgt. Carter to investigate the incidents and have a similar episode of sleepwalking after eating the rarebit.
The M*A*S*H episode "Hawk's Nightmare" features Hawkeye sleepwalking after seeing the young age of wounded soldiers he operates on. While asleep, he performs acts from his childhood such as playing basketball and marbles, then has nightmares. According to a psychiatrist, he is simply remembering an innocent time amid the horrors of war.
In both comics and TV series of Avatar: The Last Airbender Aang is shown to do numerous things in his sleep.
In the Popeye episode "A Dream Walking," Olive Oyl sleepwalks in a building construction site.
In the episode "Goodnight, Sweet Skipper" of Gilligan's Island, the occupants find that the skipper can fix the transmitter, but only while sleepwalking. They sedate the skipper in order to induce sleepwalking so as to get the transmitter fixed.
In the animated film Anastasia, Anastasia sleepwalks while on a ship in the middle of the ocean. She sleepwalks all the way to the deck of the ship during a storm, and almost falls over until Dimitri, a friend, saves her.
In an episode of The Honeymooners, Ed Norton has a sleepwalking problem, and needs help from Ralph, Alice, and Trixie to stop it. In another episode, Ed fakes a sleepwalk so Ralph has an excuse to sleep in Norton's apartment for the night. Ed would humorously sleepwalk, often taking food from Ralph's fridge and eating it.
In the universe of Supernatural TV series, werewolves are people who turn to wolves and violently kill other people while sleepwalking.
In the Law & Order: Criminal Intent episode "Consumed," (Season 3, Episode 21) a cop with a sleepwalking disorder is framed by a neighbor, a woman looking to get back at her ex-husband through murder.
In the 2013 film Side Effects, the protagonist used sleepwalking as the cover for a murder.
Because sleepwalking can result in violent behavior, legal courts sometimes deal with cases involving sleepwalkers. These cases include homicide, assault, and sexual harassment. The level of responsibility and severity of punishment has been highly debated because sleepwalkers are almost always oblivious to their activity during an episode. According to Culebras, a Professor of Neurology at the State University of New York College of Medicine, "It is conceivable that the sleepwalker has the potential to drift into a confusional arousal, a state in which violence and assault are likely when prolonged and if given the adequate circumstances. The differential diagnosis may also include other conditions in which violence related to sleep is a risk, such as REM Sleep Behavior Disorder (RSBD), fugue states, and episodic wandering." In the 1963 case Bratty v Attorney-General for Northern Ireland, Lord Morris stated, "Each set of facts must require a careful examination of its own circumstances, but if by way of taking an illustration it were considered possible for a person to walk in his sleep and to commit a violent crime while genuinely unconscious, then such a person would not be criminally liable for that act."
In the case of the law, an individual can be accused of non-insane automatism or insane automatism. The first is used as a defense for temporary insanity or involuntary conduct, resulting in acquittal. The latter results in a "special verdict of not guilty by reason of insanity." This verdict of insanity can result in a court order to attend a mental institution.
Other examples of legal cases involving sleepwalking in the defence include:
- 1981, Steven Steinberg, of Scottsdale, Arizona was accused of killing his wife and acquitted on the grounds of temporary insanity.
- 1991, R v Burgess: Burgess was accused of hitting his girlfriend on the head with a wine bottle and then a video tape recorder. Found not guilty, at Bristol Crown Court, by reason of insane automatism.
- 1992, R. v. Parks: Parks was accused of killing his mother-in-law and attempting to kill his father-in-law. He was acquitted by the Supreme Court of Canada.
- 1994, Pennsylvania v. Ricksgers: Ricksgers was accused of killing his wife. He was sentenced to life in prison without parole.
- 1999, Arizona v. Falater: Falater, of Phoenix, Arizona, was accused of killing his wife. The court concluded that the murder was too complex to be committed while sleepwalking. Falater was charged with first-degree murder, and given life sentence with no parole.
- 2008, Brian Thomas, was accused of killing his wife while he dreamt she was an intruder, whilst on holiday in West Wales. Thomas was found not guilty.
Additional bibliography 
- Nicole Edelman, Luis Montiel et Jean-Pierre Peter: Histoire sommaire de la maladie et du somnambulisme de Lady Lincoln. Paris, Tallandier, 2009.
|Wikimedia Commons has media related to: Sleepwalking|
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- Man who killed wife in sleep, Brian Thomas, walks free after charges withdrawn