In the common beliefs, Violence During Sleep evokes images of dramatic murders or suicides. However, violent or injurious behaviors during sleep are not limited to these two types of acts. A violent behavior can be harmful (or potentially harmful). It includes a broad range of behaviors: benign dream enactment (kicking, jumping out of bed, running) self-mutilation, sexual assault, murder attempt, murder and suicide.
The issue in most cases is without consequences but the behavior involves a potential danger.
The common denominator is that the sleeping violent individual is unaware of the behavior she/he is committing and has a complete amnesia of its actions.
Upon awakening, some individuals having a NREM (non-rapid eye movement sleep) parasomnia remember having frightening dream during the night but cannot provide a detailed account of the dream while in REM (rapid eye movement sleep) parasomnia, the subject can narrate the dreams upon awakening but there is also a complete amnesia of its dream enactment. These dreams are mainly centered on defending oneself against attacks from others or beasts, trying to escape a danger or to protect a loved one against potential danger.

RESEARCH

The occurrence of violent or harmful behavior during sleep is believed to be a relatively rare phenomenon. We have addressed this question in an epidemiological study (6) performed in the general population of the United Kingdom and involving 4,972 individuals 15 years old and over.

RESULTS

About 2% of respondents reported currently experiencing violent or harmful behavior during sleep with a higher occurrence in men. Night terrors, daytime sleepiness, sleep talking, bruxism, and hypnic jerks were more frequent in subjects with violent or harmful behavior during sleep than the nonviolent subjects, as were hypnagogic hallucinations (especially the experience of being attacked), the incidence of smoking, caffeine and bedtime alcohol intake.

DISCUSSION

Violent behaviors may occur in both sleep stages:

• In NREM sleep, the muscle tone is diminished but remains present allowing the sleeper to move and even to perform complex motor activities such as sleepwalking.


• In REM sleep, there is a muscle atonia, or sleep paralysis, that prevents dream enactment. Theoretically, violent behaviors during REM sleep should never occur. However, Japanese researchers have shown this safety lock is sometimes defective in humans allowing therefore the apparition of movements during REM sleep: we then assist to dream enactment in these individuals.

Violent or injurious behaviors during sleep are not an essential feature of any sleep disorder excepted for REM sleep behavior disorder, a parasomnia labeled as such by Schenck et al. in 1986 (7). However, violent behaviors have been reported in many parasomnias: confusional arousals, sleepwalking, sleep terrors, nocturnal seizures (seizures in the orbital, mesial or prefrontal region) and episodic nocturnal wanderings (epileptiform etiology suspected). About one third of assaultive acting out in sleepwalkers was associated with an episode of sleep terror.

The etiology of violent behaviors during sleep remains largely unknown in NREM parasomnias (sleepwalking, sleep terrors and confusional arousals).

In theory, episodes of sleepwalking always contain a risk of violent or harmful behaviors of any nature because the subject is moving in a surrounding with a limited perception and an unawareness of the potential dangers for self. When a night terror episode accompanies the sleepwalking, the risk of serious violence is increased. Kales et al (21) estimated that as many as 72% of persistent adult sleepwalkers are at risk of injury.

Furthermore, many conditions increase the risk of serious violence during sleep in NREM parasomnia individuals: alcohol, medication (hypnotic, tranquilizer, neuroleptic, stimulant, antihistamines) or drug intake, sleep deprivation and emotional stress (Table 1).

Table 1.Predisposing factors,precipitants and neurological diseases associated with violent or injurious behaviors during sleep

† REM Behavior Disorder only
‡ NREM parasomnias only

Male gender	Medication intake	Arnold-Chiari type I malformation
Older age	Alcohol intake	Brainstem astrocytoma
Drug intake	Dementia Irregular sleep schedule Emotional stress Sleep deprivation	Guillain-Barre Syndrome Ischemic cerebrovascular disease Lewy body disease Machado-Joseph Disease Multiple sclerosis Narcolepsy Olivo-ponto-cerebellar atrophy Parkinsonism Pontine tumor Progressive supranuclear palsy Shy-Drager Syndrome Spinocerebellar degeneration Stroke Subarachnoid hemorrhage

Men are at greater risk to have serious violent behaviors during sleep; reported homicides during sleep are almost all perpetrated by men and the wife or roommate are the most frequent victims. In the different studies, 40% of REM behavioral disorder patients had a neurological disorder directly related with the apparition of violent behaviors during sleep. A list of the neurological diseases cited in the literature can be found in Table 1. Using magnetic resonance imaging, Culbras and Moore (11) found abnormalities in the brainstem in 5 on 6 of the studied patients: lacunar infracts in periventricular white matter of both hemispheres (5 patients) and in the tegmentum of the pons in 3 patients. The increased tonic and phasic EMG activity in REM sleep found in the overwhelming majority of RBD patients are suggestive of lesions or microscopic lesions in dorsal pontomesencephalic areas.

Violent or harmful behaviors during sleep have been assumed to be indicative of and underlying severe psychopathology. In clinical studies, violent or harmful sleep behaviors have seldom been found to be the consequence of mental illness. In general, mental disorder has no etiological relationship with violent or harmful behaviors during sleep. However, a mental illness can be concomitantly present. These disorders, mostly depressive disorders, are observed in 20 to 25% of patients with harmful sleep behavior (10,12,18). Previous studies of REM Sleep Behavior Disorder (18) and sleep-related injuried patients (12) found associated psychiatric disorders in less than 10% of cases. This is further illustrated in our epidemiological study (6) where we found that the presence of a mental disorder played a significant role in explaining violent or harmful behaviors during sleep only when accompanied by other nocturnal manifestations or symptoms (e.g., sleeptalking, alcohol consumption at bedtime). Anxiety Disorder alone was nonsignificant and Mood Disorder alone presented a significantly lower risk for violent or harmful behaviors during sleep.

The genetic contribution in violent or harmful behaviors during sleep is unknown. Our study in Italy involving 3970 individuals suggests that such a contribution may exist. About one tenth of those reporting violent or harmful behaviors during sleep have a family member with similar behaviors. This rate was less than 1% in subjects without these behaviors (Ohayon M.M., data on file).

FUTURE DIRECTIONS

A growing body of literature shows that parasomnias are far more complex than what we know.
Data from epidemiological studies (22,23) and from clinical observations clearly show that mixed forms of parasomnias exist.

• For example, Kavey & Whyte (24) reported two cases of sleepwalkers who experienced hypnagogic or hypnopompic hallucinations during the episodes which resulted in lifethreatening behaviors when trying to escape from the hallucinations. Other sleep diagnoses and neurological disorders were ruled out. These appear to be a variant of the sleepwalking / night terrors association in which some individuals keep fragmentary memory of the frightening dream.
• A similar case has been reported by Hurwitz et al (25). These authors suggested that overlapping of several parasomnias may in fact represent a different parasomnia in its own.

In the general population, prevalence of parasomnias as a whole are much higher than many dyssomnias for example, obstructive sleep apnea, hypersomnia, narcolepsy. Therefore, why do sleep disorders centers have so few cases of parasomnias? This may be partly due to the fact that many individuals with violent or harmful behavior go untreated for many years before seeking medical help, persisting instead with idiosyncratic and often ineffective remedies to suppress their acting out behaviors. Frequently, individuals with such behaviors turn to health professionals only after a dramatic or harrowing experience.

Furthermore, there is a paucity of information given to the population and to the clinicians about parasomnias, their clinical manifestations and their consequences.

Further researches are needed to identify what are the best predictors of violent or harmful behaviors during sleep and how we can identify these individuals.

Our works have already provided some indications but supplemental efforts are needed to refine the knowledge of these phenomena.

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