Dissociation (psychology)

# Overview
Dissociation is a state of acute mental decompensation in which certain thoughts, emotions, sensations, and/or memories are compartmentalized because they are too overwhelming for the conscious mind to integrate. This subconscious strategy for managing powerful negative emotions is sometimes referred to as "splitting", as these thoughts, emotions, sensations, and/or memories are "split off" from the integrated ego.  This use of the word "splitting" here should not be confused with references to splitting mentioned with regard to borderline personality disorder or family relations theory.
The French psychiatrist Pierre Janet(1859-1947) initially coined the term splitting in his book L'Automatisme psychologique.  There, he emphasized its role as a defensive mechanism employed in response to psychological trauma. While he considered dissociation an initially effective defense mechanism that protects the individual psychologically from the impact of overwhelming traumatic events, a habitual tendency to dissociate would likely be a marker of a more pronounced psychopathology.
The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition considers symptoms such as depersonalization (DSM-IV Codes 300.6), derealization, and Dissociative Amnesia (DSM-IV Codes 300.12) to be core features of dissociative disorders (DSM-IV Codes Dissociative Disorders). However, in the normal population mild dissociative experiences are highly prevalent, with 60% to 65% of the respondents indicating that they have had dissociative experiences at least some of the time. 
Attention to dissociation as a clinical feature has been growing in recent years as a concomitant to knowledge of post-traumatic stress disorder, and as neuroimaging research and population studies show its relevance. Dissociation most often makes the news with regards to soldiers' responses to wartime stress, rape victims with amnesia for details, and in occasional criminal trials where the question of whether a person with Dissociative Identity Disorder (DID) can be responsible for his or her actions.
Perhaps the most widely-known form of dissociative disorder is DID, formerly known as Multiple Personality Disorder (MPD)
(see Multiple personality controversy).
Psychoactive substances can often induce a state of temporary dissociation. Substances with dissociative properties include ketamine, nitrous oxide, tiletamine, DXM and PCP.

# Dissociation in Jung's theory of the structure of the psyche.
Jung focused on the evidence of dissociation in the more or less normal individual and postulated that the psyche has structural separation of opposing faculties and tension between them. Dissociation is a natural necessity for consciousness to operate in one faculty unhampered by the demands of its opposite.
It is, in particular, the phenomena of somnambulism, double consciousness, split personality, etc., whose investigation we owe primarily to the French school, that have enabled us to accept the possibility of a plurality of personalities in one and the same individual (Jung,  1971:par. 797).
It is at once evident that such a plurality of personalities can never appear in a normal individual.  But, as the above mentioned phenomena show, the possibility of a dissociation of personality must exist, at least in the germ, within the range of the normal.  And, as a matter of fact, any moderately acute psychological observer will be able to demonstrate, without much difficulty, traces of character-splitting in normal individuals. ... In accordance with social conditions and requirements, the social character is oriented on the one hand by the expectations and demands of society, and on the other by the social aims and aspirations of the individual. ... Which is the true character, the real personality?  This question is often impossible to answer (Jung,  1971:par. 798).
These reflections show that even in normal individuals character-splitting is by no means an impossibility.  We are, therefore, fully justified in treating personality dissociation as a problem of normal psychology (Jung,  1971:par. 799).
The structural dissociation, opposing tension, and hierarchy of basic attitudes and functions in normal individual consciousness is the basis of Jung's Psychological Types. He describes the positive traits of each theoretically "pure" type ("pure" meaning completely depending on the conscious use of the dominant psychological function and attitude, and completely repressing or dissociating the opposing structural function and attitude). He also describes in detail the devastating pathological effects of each pure type's ignorance of the autonomous unconsciousness operation and opposing archaic influence of its inferior function and attitude.
Jung's theory explains pathological manifestions of dissociation as special or extreme cases of the normal operation of the psyche.