Dissociation is a mechanism that allows the mind to separate or compartmentalise certain memories or thoughts from normal consciousness. These split-off mental contents are not erased. They may resurface spontaneously or be triggered by objects or events in the person’s environment.
Dissociation is a process that occurs along a spectrum of severity. If someone experiences dissociation, it does not necessarily mean that that person has a dissociative disorder or other mental illness. A mild degree of dissociation occurs with some physical stressors; people who have gone without sleep for a long period of time, have had “laughing gas” for dental surgery, or have been in a minor accident often have brief dissociative experiences. Another commonplace example of dissociation is a person becoming involved in a book or movie so completely that the surroundings or the passage of time are not noticed. Another example might be driving on the highway and taking several exits without noticing or remembering. Dissociation is related to hypnosis in that hypnotic trance also involves a temporarily altered state of consciousness. Most patients with dissociative disorders are highly hypnotisable.
People in other cultures sometimes have dissociative experiences in the course of religious (in certain trance states) or other group activities.
Moderate or severe forms of dissociation are caused by such traumatic experiences as childhood abuse , combat, criminal attacks, brainwashing in hostage situations, or involvement in a natural or transportation disaster. Patients with acute stress disorder , post-traumatic stress disorder (PTSD), conversion disorder, or somatisation disorder may develop dissociative symptoms. Recent studies of trauma indicate that the human brain stores traumatic memories in a different way than that of normal memories. Traumatic memories are not processed or integrated into a person’s ongoing life in the same fashion as normal memories. Instead they are dissociated, or “split off,” and may erupt into consciousness from time to time without warning. Over a period of time, these two sets of memories, the normal and the traumatic, may coexist as parallel sets without being combined or blended. In extreme cases, different sets of dissociated memories may cause people to develop separate personalities for these memories – a disorder known as dissociative identity disorder (formerly called multiple personality disorder).