Neurobiology of Parasomnias

Parasomnias are undesirable physical or psychical events that accompany sleep. They are classified according to the sleep state of origin in rapid eye movement (REM)-related parasomnias, non-REM (NREM)-related parasomnias, and other parasomnias, without any link with a specific sleep stage. Parasomnias are a heterogeneous group of manifestations that can result from very different etiologies. In most cases they are diagnosable and treatable. REM sleep behavior disorder (RBD), a REM parasomnia, can be a predictive marker of neurodegenerative diseases. The pathophysiology of parasomnia is only partially understood and in some cases is not known. Yet, in the two main groups of parasomnic manifestations, i.e., the disorders of arousal (DOA) and RBD, the foremost mechanism is a state dissociation during which the brain is partially awake and partially asleep. The result is a mixed state of being in which the individual is capable of performing very complex behaviors but is not aware of his actions. Additionally, the involvement of other mechanisms, such as the inappropriate activation of central pattern generators (CPGs), has been proposed.