common in children with an estimated 5%, compared with 1.5% of adults, sleepwalking at least once in the previous 12 months. the rate of sleepwalking has not been found to vary across ages during childhood. history sleepwalking has attracted a sense of mystery, but was not seriously investigated and diagnosed until the 19th century. the german chemist and parapsychologist baron karl ludwig von reichenbach (1788–1869) 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). 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 clarified and expanded his hypothetical ideas on dreams. he described the dream as a fragile equilibrium that is destabilized by the repressed unconscious impulses of the unconscious system, which does not obey the wishes of the ego. certain preconscious daytime thoughts can be resistant and these can retain a part of their cathexis as well. unconscious impulses and day residues can come together and result in a conflict. freud then wondered about the outcome of this wishful impulse: an unconscious instinctual demand that becomes a dream wish in the preconscious. 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. as of 2002, sleepwalking has not been detected in non-human primates. it is unclear whether it simply has not been observed yet, or whether sleepwalking is a uniquely human phenomenon. society and culture opera amina, the somnabuliste, at the mill. vincenzo bellini's 1831 italian opera semiseria, la sonnambula, the plot of which is centered on the question of the innocence of the betrothed and soon-to-be married amina, who, upon having been discovered in the bedchamber of a stranger, and despite the assurances of that stranger that amina was entirely innocent, has been rejected by her enraged fiancé, elvino — who, then, decides to marry another. in fact, when stressed, amina was susceptible to somnambulism; and had come to be in the stranger's bedchamber by sleep-walking along a high parapet (in full view of the opera's audience). elvino, who later observes the (exhausted by all the fuss) amina, sleep-walking across a very high, very unstable, and very rickety bridge at the local mill, realizes his mistake, abandons his plans of marriage to the other woman, and re-unites with amina. jenny lind and james braid in august 1847, the famous soprano jenny lind visited manchester, and gave two performances as amina. the outstanding difference between lind and her contemporaries was that, "whilst the beauty of her voice was far greater than any other in living memory (thus, the swedish nightingale), what really set her apart was her outstanding ability to act"; and, moreover, in performing as amina, rather than walking along a wide and well-protected walkway (as the others did), she routinely acrobatically balanced her way along narrow planks. while she was in manchester—on the basis that, at the time, many characterized "hypnotism" as "artificial somnambulism", and that, from a rather different perspective, her stage performance could also be described as one of "artificial" (rather than spontaneous) somnambulism—her friends arranged for her to visit the local surgeon james braid, who had discovered hypnotism in 1841: mr. braid, surgeon, whose discoveries in hypnotism are well known, having invited the fair impersonator of a somnambulist to witness some of the abnormal feats of a real somnambulist, artificially thrown into that state, it was arranged that a private séance should take place .— manchester guardian, 8 september 1847 drama mary hoare's painting lady macbeth, sleepwalking the sleepwalking scene (act v scene 1) from william shakespeare's tragic play macbeth (1606) is one of the most famous scenes in all of literature. in walley chamberlain oulton's two act farce the sleep-walker; or, which is the lady (1812), "somno", a histrionic failed-actor-turned-manservant relives his wished-for roles when sleepwalking. literature in bram stoker's novel dracula, the character lucy westenra is described as a sleepwalker. it is while sleepwalking that count dracula lures and attacks her. sleepwalking as a legal defense as sleepwalking behaviours occur without volition, sleepwalking can be used as a legal defense, as a form of legal automatism. an individual can be accused of non-insane 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. in the 1963 case bratty v a-g 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." while the veracity of the cases are disputed, there have been acts of homicide where the prime suspect may have committed the act while sleepwalking. alternative explanations to homicidal or violent sleepwalking include malingering, drug-induced amnesia, and other disorders in which sleep-related violence may occur, such as rem sleep behavior disorder, fugue states, and episodic wandering. "the boston tragedy," the murder of maria bickford, 1846; tirrell was acquitted because of sleepwalking. national police gazette, 1846 historical cases 1846, albert tirrell used sleepwalking as a defense against charges of murdering maria bickford, a prostitute living in a boston brothel. 1961, sergeant willis boshears confessed to strangling a local woman named jean constable in the early hours on new years day 1961, but claimed that he was asleep and only woke to realize what he had done. he pled not guilty on the basis of being asleep at the time he committed the offence and was acquitted. in 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. he was 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: scott 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 convicted of first-degree murder and sentenced to life with no possibility of parole. 2001, california v. reitz: stephen reitz killed his lover, eva weinfurtner. he told police he had no recollection of the attack but he had "flashbacks" of believing he was in a scuffle with a male intruder. his parents testified in court that he had been a sleepwalker from childhood. the court convicted reitz of first-degree murder in 2004. in 2001, antonio nieto murdered his wife and mother-in-law and attempted to murder his daughter and son, before being disarmed. nieto claimed to have been asleep during the attack and dreaming that he was defending himself against aggressive ostriches. however, his children stated that he had recognized them and had told his son to not turn on the lights because their mother (gravely injured already) was sleeping. in 2007, nieto was sentenced to 10 years internment in a psychiatric hospital and ordered to pay 171,100 euros as compensation to the victims. jules lowe confessed to causing the death of his father edward in 2004, but did not remember committing the act. jules used automatism as his defense, and was found not guilty by reason of insanity and detained indefinitely in a secure hospital. he was released after ten months. brian thomas was accused of killing his wife in 2008 while dreaming that he was fighting off intruders. he was freed in 2009 by a judge, who found him not guilty of murder.