SOMNAMBULISM (from Lat. scannas, sleep ambulare, to walk). A state intermediate be tween those of sleeping and waking, character ized by the performance of various acts appar ently indicative of conscious control, by absence of the usual reaction to stimuli, and usually by inability to recall on awakening any of the thoughts or movements which have taken place during the abnormal condition. Somnambulism may he self-induced, spontaneous. o• idiopathic, or artificially induced• as in the hypnotic trance. In the latter sense, the term is popularly used as a synonym of hypnosis, hut strictly speaking it should he limited in accordance with its defi nition by the 'Paris school,' who apply the term only to the 'third stage' of the hypnotic state. (See lIrrNonsm.) In this, the final stage, the subject is almost completely anesthetic, obeys or ders by movement and perception. and, when awakened, has no memory at all of what has elapsed during the somnambulistic period.
Spontaneously induced somnambulism of a mild or imperfect type is frequent. It is most obviously, though perhaps not most strikingly, manifested by persons who walk at night during sleep. A slight stimulus, enough to vale!: the at
tention, will restore the normal condition. In its pronounced form, often exhibited by patients suffering from hysteria, somnambulism approach es, if it does not cross, the border-line between the merely anomalous and the abnormal or patho logical. Psychologically, sleep-walking is only a dream carried one step beyond its usual limita tions. In dream-walking the barrier to execu tion is partially lifted, and the conditions of nor mal connection between idea and movement are fulfilled. Somnambulism further differs from normal sleep in that, within certain limits, there is in it cognizance of external objects. The som nambulist may walk the ridge-pole thinking it a boulevard, but his actions are confined to rela tively simple acts, which, like walking, have be come automatic by practice.
Consult: Take, Sleep-Walking and Hypnotism• (London, 1884); Liegois, Dc la suggestion ct somnambulisme lour rapport avec to juris prudence et la medecine legale (Paris, 1889) ; W. Wundt, Lectures on Haman and Animal Psychol ogy, trans. (New York, 1894).