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 experience. It is commonly displayed on a continuum. The major characteristic of all dissociative phenomena involves a detachment from reality – rather than a loss of reality as in psychosis. 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. 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.
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 (depersonalization and derealization); 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. Dissociative disorders are sometimes triggered by trauma, but may be preceded only by stress, psychoactive substances, or no identifiable trigger at all. The ICD-10 classifies conversion disorder as a dissociative disorder. The Diagnostic and Statistical Manual of Mental Disorders groups all dissociative disorders into a single category.
Although some dissociative disruptions involve amnesia, other dissociative events do not. 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 (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. 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.
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. 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.
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. 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.
Measurement and diagnosis of 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. 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. The SCID-D is a structured interview used to assess and diagnose dissociation.
Relation to trauma and abuse 
Dissociation has been described as one of a constellation of symptoms experienced by some victims of multiple forms of childhood trauma, including physical, psychological, and sexual abuse. This is supported by studies which suggest that dissociation is correlated with a history of trauma. Dissociation appears to have a high specificity and a low sensitivity to having a self-reported history of trauma, which means that dissociation is much more common among those who are traumatized, yet at the same time there are many persons who have suffered from trauma but who do not show dissociative symptoms.
Adult dissociation when comorbid with a history of child abuse and otherwise interpersonal violence-related posttraumatic stress disorder (PTSD) has been shown to contribute to disturbances in parenting behavior, such as exposure of young children to violent media. Such behavior may contribute to cycles of familial violence and trauma.
Symptoms of dissociation resulting from trauma may include depersonalization, psychological numbing, disengagement, or amnesia regarding the events of the abuse. It has been hypothesized that dissociation may provide a temporarily effective defense mechanism in cases of severe trauma; however, in the long term, dissociation is associated with decreased psychological functioning and adjustment. Other symptoms sometimes found along with dissociation in victims of traumatic abuse (often referred to as "sequelae to abuse") include anxiety, PTSD, low self-esteem, somatization, depression, chronic pain, interpersonal dysfunction, substance abuse, self-mutilation and suicidal ideation or actions. These symptoms may lead the victim to erroneously present the symptoms as the source of the problem.
Child abuse, especially chronic abuse starting at early ages, has been related to high levels of dissociative symptoms in a clinical sample, including amnesia for abuse memories. A non-clinical sample of adult women linked increased levels of dissociation to sexual abuse by a significantly older person prior to age 15, and dissociation has also been correlated with a history of childhood physical and sexual abuse. When sexual abuse is examined, the levels of dissociation were found to increase along with the severity of the abuse.
A 2012 review article supports the hypothesis that current or recent trauma may affect an individual's assessment of the more distant past, changing the experience of the past and resulting in dissociative states.
Psychoactive substances 
Psychoactive drugs can often induce a state of temporary dissociation. Substances with dissociative properties include ketamine, nitrous oxide, alcohol, LSD, tiletamine, marijuana, dextromethorphan, MK-801, PCP, methoxetamine, salvia, muscimol, atropine, and ibogaine.
See also 
- Altered state of consciousness
- Coping (psychology)
- Dissociative disorder
- Dissociative Experiences Scale
- Dissociative Identity Disorder
- Dissociative substance
- Emotional detachment
- Fantasy prone personality
- International Society for the Study of Trauma and Dissociation
- Psychological numbing
- Repressed memory
- Splitting (psychology)
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- The official journal of the International Society for the Study of Dissociation (ISSD), published between 1988 and 1997