State that resembles sleep but is induced by a person (the hypnotist) whose suggestions are readily accepted by the subject. The hypnotized individual seems to respond in an uncritical, automatic fashion, ignoring aspects of the environment (e.g., sights, sounds) not pointed out by the hypnotist. Even the subject's memory and awareness of self may be altered by suggestion, and the effects of the suggestions may be extended (posthypnotically) into the subject's subsequent waking activity. The history of hypnotism is as old as that of sorcery and magic. It was popularized in the 18th century by Franz Anton Mesmer (as mesmerism) and was studied in the 19th century by the Scottish surgeon James Braid (1795–1860). Sigmund Freud relied on it in exploring the unconscious, and it eventually came to be recognized in medicine and psychology as useful in helping to calm or anesthetize patients, modify unwanted behaviours, and uncover repressed memories. There remains no generally acceptable explanation for hypnosis, though one prominent theory focuses on the possibility of discrete dissociative states affecting portions of consciousness.