Dissociation is a term in psychology describing a wide array of experiences from mild detachment from immediate surroundings to more severe detachment from physical and emotional reality. It is commonly displayed on a continuum.[1] The major characteristic of all dissociative phenomena involves a detachment from reality rather than a loss of reality as in psychosis.[2][3][4][5] In mild cases, dissociation can be regarded as a coping mechanism or defense mechanisms in seeking to master, minimize or tolerate stress including boredom or conflict.[6][7][8] At the nonpathological end of the continuum, dissociation describes common events such as daydreaming while driving a vehicle. Further along the continuum are non-pathological altered states of consciousness.[1][9][10] More pathological dissociation involves dissociative disorders, including dissociative fugue and depersonalization disorder with or without alterations in personal identity or sense of self. These alterations can include: a sense that self or the world is unreal (derealization and depersonalization); a loss of memory (amnesia); forgetting identity or assuming a new self (fugue); and fragmentation of identity or self into separate streams of consciousness (dissociative identity disorder, formerly termed multiple personality disorder) and complex post-traumatic stress disorder.[11][12] Dissociative disorders are sometimes triggered by trauma, but may be preceded only by stress, psychoactive substances, or no identifiable trigger at all.[13] The ICD-10 classifies conversion disorder as a dissociative disorder.[1] The Diagnostic and Statistical Manual of Mental Disorders groups all dissociative disorders into a single category.[14] Although some dissociative disruptions involve amnesia, other dissociative events do not.[15] Dissociative disorders are typically experienced as startling, autonomous intrusions into the person's usual ways of responding or functioning. Due to their unexpected and largely inexplicable nature, they tend to be quite unsettling.

The French philosopher and psychiatrist Pierre Janet (18591947) is considered to be the author of the concept of dissociation.[16] Contrary to some conceptions of dissociation, Janet did not believe that dissociation was a psychological defense.[17][18] Psychological defense mechanisms belong to Freud's theory of psychoanalysis, not to Janetian psychology. 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 efficiency" of a hysteric, thereby generating a cascade of hysterical (in today's language, "dissociative") symptoms.[16][19][20][21] 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 [16]. Even Janet largely turned his attention to other matters. On the other hand, 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. Nevertheless, even in America, interest in dissociation rapidly succumbed to the surging academic interest in psychoanalysis and behaviorism. For most of the twentieth century, there was little interest in dissociation. Discussion of dissociation only resumed when Ernest Hilgard (1977) published his neodissociation theory in the 1970s and when several authors wrote about multiple personality in the 1980s.[citation needed] Carl Jung described pathological manifestations of dissociation as special or extreme cases of the normal operation of the psyche. This structural dissociation, opposing tension, and hierarchy of basic attitudes and functions in normal individual consciousness is the basis of Jung's Psychological Types.[22] He theorized that dissociation is a natural necessity for consciousness to operate in one faculty unhampered by the demands of its opposite. Attention to dissociation as a clinical feature has been growing in recent years as knowledge of post-traumatic stress disorder increased, due to interest in dissociative identity disorder and the multiple personality controversy, and as neuroimaging research and population studies show its relevance.[23] Main article: dissociative disorder Dissociation in community samples is most commonly measured by the Dissociative Experiences Scale. The DSM-IV considers symptoms such as depersonalization, derealization and psychogenic amnesia to be core features of dissociative disorders.[24] However, in the normal population dissociative experiences that are not clinically significant are highly prevalent, with 60% to 65% of the respondents indicating that they have had some dissociative experiences.[25] The SCID-D is a structured interview used to assess and diagnose dissociation.