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==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.