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Mark Mahowald (2006), Scholarpedia, 1(12):2427. doi:10.4249/scholarpedia.2427 revision #91623 [link to/cite this article]
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Curator: Mark Mahowald

The term parasomnias refers to a variety of conditions characterized by complex behaviors arising from the sleep period without conscious awareness. The most common are:

  1. disorders of arousal (confusional arousals, sleepwalking, and sleep terrors) and
  2. REM (rapid-eye movement) sleep behavior disorder (RBD).

The concept of "state dissociation" explains these parasomnias. As mammals, we spend our existence in one of three states of being: wakefulness, non-rapid-eye movement (NREM) sleep, or rapid-eye movement (REM) sleep. Importantly, these states are not mutually exclusive, and portions of one state may intrude into another - resulting in combinations of wake and sleep. The disorders of arousal represent an admixture of wakefulness and NREM sleep; RBD is a mixture of wakefulness and REM sleep.


Disorders of arousal

The disorders of arousal occur on a broad spectrum, ranging from confusional arousals, sleepwalking, or sleep terrors. They share common features: they tend to arise from slow-wave sleep (stages 3 and 4 of NREM sleep) - therefore usually occurring in the first third of the sleep cycle (and rarely during naps). They are very common in childhood - usually decreasing in frequency with increasing age. There is often a family history of disorders of arousal. Some take the form of "specialized" behaviors such as sleep-related eating and sleep-related sexual activity - without conscious awareness.

Confusional arousals

These are often seen in children, and are characterized by movements in bed, occasionally thrashing about, or inconsolable crying. The prevalence of confusional arousals in adults is approximately 4%.


Sleepwalking is prevalent in childhood (1-17%) peaking at 11-12 years of age and is far more common in adults (nearly 4%) than generally acknowledged. Sleepwalking may be either calm or agitated, with varying degrees of complexity and duration. Sleepwalking behaviors may be complex and protracted such as rearranging furniture, driving an automobile, or walking to a neighbor's house.

Sleep terrors

Sleep terrors are the most dramatic disorder of arousal. They are frequently initiated by a loud, blood-curdling scream associated with extreme panic, followed by prominent motor activity such as hitting the wall, running around or out of the bedroom, even out of the house - resulting in bodily injury or property damage. A universal feature is inconsolability. Although the victim appears to be awake, he/she usually misperceives the environment, and attempts at consolation are fruitless and may serve only to prolong or even intensify the confusional state. Some degree of perception may be evident, for example: running for and opening a door or window. Complete amnesia for the activity is typical, but may be incomplete. Although usually benign, these behaviors may be violent, resulting in considerable injury to the victim or others or damage to the environment - occasionally with forensic implications.

Disorders of arousal may be primed or potentiated by febrile illness, alcohol, prior sleep deprivation, physical activity, or emotional stress. Medication-induced cases have been reported with sedative/hypnotics, major or minor tranquilizers, stimulants, and antihistamines, often in combination with each other.

Episodes of sleep terrors may be provoked or triggered by stimuli such as snores, irregular breathing, apneas or hypopneas, leg movements, noise or touch.

Persistence of these behaviors beyond childhood or their development in adulthood is often taken as an indication of significant psychopathology. Several studies have questioned the strength of this association, indicating that severe psychopathology is usually not present in adults with disorders of arousal. However, psychological factors may still play a role in the expression of these disorders in some patients, and the physiological mechanism of these disorders more generally remains unclear. Both genetic and environmental factors are operant.

These arousals may not be the culmination of ongoing psychologically significant mentation, in that somnambulism can be induced in normal children by standing them up during slow-wave sleep and sleep terrors can be precipitously triggered in susceptible individuals by sounding a buzzer during slow-wave sleep.

Given the high prevalence of these disorders in normal individuals, formal sleep center evaluation should be confined to those cases in which the behaviors are potentially injurious or violent, are extremely bothersome to other household members, result in symptoms of excessive daytime sleepiness, or have unusual clinical characteristics.

Treatment is often not necessary. Reassurance of their typically benign nature, lack of psychological significance, and the tendency to diminish over time, is often sufficient. The tricyclic antidepressants and benzodiazepines may be effective, and should be administered if the behaviors are dangerous to person or property or extremely disruptive to family members. Nonpharmacologic treatment such as psychotherapy, progressive relaxation, or hypnosis is recommended for long-term management. The avoidance of precipitants such as drugs, alcohol, and sleep deprivation is also important.

REM sleep behavior disorder (RBD)

RBD is a fascinating experiment in nature predicted by animal experiments in 1965. Cats with bilateral lesions in the brainstem demonstrated prominent motor activity during REM sleep. A defining feature of REM sleep is active paralysis of all somatic musculature (except the diaphragm which permits respiration during REM sleep). This paralysis may be a good thing, as brain activity may be greater during REM sleep than during wakefulness. Were we not paralyzed during REM sleep, we could have the ability to "act out our dreams".

The supraspinal mechanisms responsible for REM-atonia originate in the perilocus ceruleus (LC)-alpha nucleus in the pons that excite neurons of the nucleus reticularis magnocellularis in the medulla, which then transmit descending inhibitory projections--more powerful than the competing descending excitatory projections. Loss of REM-atonia is alone insufficient to generate RBD. Presumably, there must also be disinhibition of motor pattern generators in the mesencephalic locomotor region to result in over-excitation of phasic motor activity with behavioral release during REM.

The typical complaint of a patient with RBD is violent dream-enacting behavior which are potentially injurious to the individual or bed partner. There are acute and chronic forms of RBD.

Acute RBD is almost always induced by medications (tricyclic antidepressants, monoamine oxidase inhibitors, SSRIs, venlafaxine, or associated with withdrawal of sedatives such as alcohol, barbiturates, or meprobamate.

The chronic form is seen most frequently in men (80-90%) over 50 years of age, although females and virtually all age groups are represented. One fourth of the patients have a prodrome, often lengthy, involving subclinical behavioral (vocal and/or motor) release during sleep. Many patients with RBD report that dreams have become more vivid and "action‑packed" coincident with the onset of the dream‑enacting behavior.

Complex RBD behaviors are generally aggressive or exploratory, and never appetitive (feeding, sexual). There is a strong link between altered dreams and dream-enacting behaviors, suggesting a mutual pathophysiology: patients do not enact their customary dreams, but rather they enact distinctly altered dreams, usually involving confrontation, aggression, and violence.

A recent phone survey of over 4900 individuals between the ages of 15 and 100 years of age indicated an overall prevalence of violent behaviors in general during sleep of 2%, one-quarter of which were likely due to RBD, giving an overall prevalence of RBD at 0.5% RBD most frequently presents with the complaint of dramatic, violent, potentially injurious motor activity during sleep. These behaviors include talking, yelling, swearing, grabbing, punching, kicking, jumping, or running out of the bed. Injuries are not uncommon and include ecchymoses, lacerations, or fractures involving the individual or bed partner. The violence of the sleep‑related behavior is often discordant with the waking personality. The reported motor activity usually correlates with remembered dream mentation, leading to the complaint of "acting out my dreams." Less frequently, the primary complaint is one of sleep interruption. The duration of behaviors is brief, and upon awakening from an episode there is usually rapid return of alertness and orientation. Some patients adopt extraordinary measures to prevent injury during sleep: they may tether themselves to the bed with a rope or belt, sleep in sleeping bags, or sleep on a mattress on the floor in a room without furniture.

Due to its association with REM sleep, the timing of the behaviors during the sleep period ranges from 90 minutes after sleep onset to the final awakening in the morning. RBD rarely occurs during daytime naps in that REM sleep during naps is exceptional. The frequency of the episodes ranges from once every few weeks to multiple nightly episodes. Complications include fractures, lacerations, and ecchymoses. Sleep‑related violence may have forensic science implications.

Systematic study of patients with neurologic syndromes indicates that RBD and REM sleep without atonia may be far more prevalent than previously suspected. The chronic form of RBD may be idiopathic. The remainder are associated with various neurologic disorders, most notably the synucleinopathies (Parkinson's disease, multiple system atrophy - including olivopontocerebellar degeneration and the Shy-Drager syndrome, and dementia with Lewy bodies disease). RBD may actually precede the appearance of other symptoms of these disorders by a decade or more. Although the prevalence of RBD in Parkinson's disease is unknown, subjective reports indicate that 25% of patients with Parkinson's disease have behaviors suggestive of RBD or sleep-related injurious behaviors, and formal sleep studies found RBD in nearly half of patients with Parkinson’s disease with sleep complaints.

Narcolepsy is also a risk factor for the development of RBD. Furthermore, tricyclic antidepressants, MAOIs, and SSRIs, used to treat cataplexy associated with narcolepsy, can trigger or exacerbate RBD in this population.

The acute form is self‑limited following discontinuation of the offending medication or completion of withdrawal. About 90% of patients with chronic RBD respond well to clonazepam administered one‑half hour prior to sleep time. The dose ranges from 0.5 to 2.0 mg, and there has been little, if any, tendency to develop tolerance, dependence, abuse, or adverse sleep effects despite years of continuous administration and efficacy. Melatonin or pramipexole may also be effective.

In summary, complex, occasionally violent behaviors arising from the sleep period are common, and are not usually related to psychiatric conditions. Most are due to admixed states of wakefulness and sleep and are without conscious awareness. Most are diagnosable, and readily treatable.


(Selected Bibliography)

  1. Cramer Bornemann MA, Mahowald MW, Schenck CH. Parasomnias. Clinical features and forensic implications. Chest. 2006;130:605-610.
  2. Mahowald MW, Schenck CH. NREM sleep parasomnias. Neurologic Clinics. 2005;23:1077-1106.
  3. Schenck CH, Mahowald MW. REM sleep parasomnias. Neurologic Clinics. 2005;23:1107-1126.

External links

See also

Dreaming, Narcolepsy, REM (Paradoxical) Sleep, Sleep, Sleep and Learning, Sleep Deprivation, Sleep Homeostasis, Sleep-walking, Slow Wave Sleep

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