Dissociation is a concept that has been developed over time and which concerns a wide array of experiences, ranging from a mild emotional detachment from the immediate surroundings, to a more severe disconnection from physical and emotional experiences. The major characteristic of all dissociative phenomena involves a detachment from reality, rather than a loss of reality as in psychosis.
The phenomena are diagnosable under the DSM-5 as a group of disorders as well as a symptom of other disorders through various diagnostic tools. Its cause is believed to be related to neurobiological mechanisms, trauma, anxiety, and psychoactive drugs. Research has further related it to suggestibility and hypnosis, and it is inversely related to mindfulness, which is a potential treatment.
French philosopher and psychologist Pierre Janet (1859–1947) is considered to be the author of the concept of dissociation. Contrary to some conceptions of dissociation, Janet did not believe that dissociation was a psychological defense.
Janet claimed that dissociation occurred only in persons who had a constitutional weakness of mental functioning that led to hysteria when they were stressed. Although it is true that many of Janet's case histories described traumatic experiences, he never considered dissociation to be a defense against those experiences. Quite the opposite: Janet insisted that dissociation was a mental or cognitive deficit. Accordingly, he considered trauma to be one of many stressors that could worsen the already-impaired "mental deficiency" of a hysteric, thereby generating a cascade of hysterical (in today's language, "dissociative") symptoms.
Although there was great interest in dissociation during the last two decades of the nineteenth century (especially in France and England), this interest rapidly waned with the coming of the new century. Even Janet largely turned his attention to other matters. There was a sharp peak in interest in dissociation in America from 1890 to 1910, especially in Boston as reflected in the work of William James, Boris Sidis, Morton Prince, and William McDougall.