THE TERM 'HYPNOSIS' was coined by the Scottish physician James Braid in his 1853 book Neurypnology. Braid defined hypnosis as "a peculiar condition of the nervous system, induced by a fixed and abstracted attention of the mental and visual eye". He argued that hypnosis was a form of "nervous sleep", and tried to distinguish his theory from that of the mesmerists, who believed that the effects of hypnosis were mediated by a vital force, or animal magnetism.

Because of mesmerism, and its association with stage entertainment and charlatanry, hypnosis was regarded with skepticism for much of its history. In recent years, though, it has come under the scrutiny of cognitive neuroscientists, and is now thought of as an altered state of consciousness - sometimes referred to as being trance-like - which is associated with increased suggestibility, enhanced imagery and reduced reality testing.