NREM Arousal Parasomnias

Abstract

Episodes of somnambulism have been described as far back as the ancient Greeks. Lacking our current knowledge of sleep and sleep disorders, these episodes no doubt included conditions other than the nonrapid eye movement (NREM) arousal parasomnias—sleepwalking (somnambulism), sleep terrors, and confusional arousals. Epilepsy, rapid eye movement (REM) behavior disorder, dissociative disorder, and other causes of nocturnal wandering were no doubt the source of many behaviors labeled as somnambulism. Until the 1930s, somnambulism was often attributed to religious or supernatural causes. Until the 1960s, somnambulism was attributed to acting out of dreams. Psychodynamic theory in the first half of the twentieth century attributed it to unresolved psychic trauma. Several nineteenth-century writers, while attributing somnambulism to dreaming, made accurate clinical descriptions and even ventured physiological explanations similar to modern theories. The first scientific research was conducted in 1884. In 1963, the first sleep-laboratory-based studies of somnambulism were conducted and to the researchers’ surprise they found that the complex behaviors in sleep were not associated with the recently described REM sleep or with REM-sleep-related dreaming. Rather, it occurred following a partial arousal from deep sleep. This eventually led in 1968 to a description of somnambulism and related disorders as “disorders of arousal.” This continues to form the basis of our understanding of NREM arousal parasomnias until this day. Hundreds of research studies have since followed. NREM arousal disorders can now be provoked in the sleep laboratory by sleep deprivation and acoustic stimuli for research purposes. Standards for differential diagnosis have been published. The underlying theory of NREM arousal disorders now involves evidence showing a dissociation of different brain areas during sleep and the fact that some parts of the brain may be technically awake while others are asleep.