Case report
Somnambulistic sexual behaviour (sexsomnia)

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Abstract

Somnambulism or sleepwalking is a viable defence on the basis of automatism. The behaviours that occur during sleepwalking can be highly complex and include sexual behaviour of all types. Somnambulistic sexual behaviour (also called sexsomnia, sleep sex) is considered a variant of sleepwalking disorder as the overwhelming majority of people with Sexsomnia have a history of parasomnia and a family history of sleepwalking. Sexual behaviour during a sleep automatism can vary from explicit sexual vocalisations, to violent masturbation, to complex sexual acts including anal, oral and vaginal penetration. A recent case in England is reported where the defendant was acquitted on 3 charges of rape on the basis of automatism due to somnambulistic sexual behaviour.

Introduction

Sexual behaviour during sleep is rarely reported in the literature and generally it is not mentioned when violence during sleep is reported. In 1986, Wong reported the case of a 34-year-old man with episodes of nocturnal masturbation that he considered “somnambulism variant”.1 Further reports were cited in abstracts of individuals who engaged in sleep-related sexual behaviour, all of whom had prior histories of parasomnia.2, 3 A comprehensive account of sexual behaviour in the forensic context was provided by Fenwick in a landmark paper in 1996.4 Subsequently, a case report was published suggesting an overlap between the syndromes of rapid eye movement (REM) sleep behaviour disorder (RBD) and somnambulism.5 In 1998, a further forensic case of somnambulistic sexual behaviour was reported, that of a 45 year old man with a history of sleepwalking being accused of fondling his daughter’s friend.6 More recently two case series were published independently by two authorities in the field.7, 8 All the patients were identified as having an underlying sleep disorder with automatic behaviour. These disorders included: (1) disorders of arousal (non-REM parasomnias) that include confusional arousal, sleep terror, and sleepwalking; (2) REM sleep behaviour disorder (RBD); (3) nocturnal partial complex seizures; (4) obstructive sleep apnoea (OSA). In a significant proportion of cases, underlying psychopathology was also present.

Section snippets

Case report – JB

JB was a 22 year old male, employed in information services at the time of his arrest in early 2005. He was woken by police at approximately 10.30 am and arrested on suspicion of rape. He did not seek legal counsel and reported consistently during his police interviews that he had no recollection of any of the events for which he was subsequently charged. JB was charged with three counts of rape, i.e., anal, vaginal and oral rape. All three acts occurred in sequence over a period of a few

Somnambulism, automatism and the law

A sleepwalking episode is known as a sleep transition disorder because the episode occurs when the brain is switching over from deep slow wave sleep to REM sleep. Thus many sleepwalking episodes occur between one and 2 h after sleep onset. The most commonly implicated sleep disorders associated with automatism are the Parasomnias of which the Disorders of Arousal are the most common. These include sleepwalking disorder, Sleep Terror Disorder, Nocturnal Sleep Drunkenness (also called confusional

Medical guidelines for sleep-related violence

To assist in the determination of the causative role of an underlying sleep disorder in a specific violent act, the following proposed guidelines have been compiled in the medical literature.9, 10, 11

  • There should be reason (by history or formal sleep laboratory evaluation) to suspect a bona fide sleep disorder. Similar episodes, with benign or morbid outcome, should have previously occurred.

  • There is evidence of lack of awareness on the part of the individual during the event.

  • The victim is

The diagnosis of sleepwalking in the forensic context

The following criteria are now generally regarded as essential for a diagnosis of sleepwalking in the forensic context:4, 9

Objective tests

In the forensic arena specific objective criteria become more important, to make it clear in court that this defence is not one which has just been dreamed up optimistically by the defendant.

Effects of alcohol on sleep

Alcohol causes a more rapid sleep induction (its hypnotic effect) in normal subjects, and a lengthening of the deep sleep cycle. It also has a unique effect on sleep in the later part of the night as the drug is metabolised and cleared from the body. During this sleep period, subjects show increased waking or light sleep, the so-called ‘metabolic rebound’. This is a common phenomenon in most people who consume alcohol, leading to them being wide awake or in a light sleep about 2–3 h after

Sleep disordered breathing and parasomnias

There is now significant clinical and published evidence that there is a complex relationship between parasomnias and sleep disordered breathing such as obstructive sleep apnoea.18 It is now established that parasomnias such as sleepwalking and night terrors can be precipitated by sleep disordered breathing. In addition, it has been shown that patients with parasomnia disorders have an increased rate of respiratory events in sleep.19 Another important finding of this study is that respiratory

Conclusions

The case of JB highlights many issues from both a medical and legal perspective. The prevalence of sexual behaviour in sleep is unknown, and as such the prevalence of harmful sexual behaviour in sleep is also unknown. Although it is accepted that physiologically it is not possible to have an erection in stage 4 sleep, as somnambulistic episodes occur out of stage 3 and 4 sleep, the presence of an erection is not considered an exclusion criteria for sleepwalking.8 Previous case reports and case

Competing interests

IE acted as an expert for the defence in the above case.

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This paper is part of the special issue entitled “Sexual offences”, guest edited by Dr. Guy Norfolk and Dr. Cath White.

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