Many people occasionally experience a failure in the normal automatic integration of memories, perceptions, identity, and consciousness. For example, people may drive somewhere and then realize that they do not remember many aspects of the drive because they were preoccupied with personal concerns, a program on the radio, or conversation with a passenger. Typically, such a failure, referred to as nonpathologic dissociation, does not disrupt everyday activities.
In contrast, people with a dissociative disorder may totally forget a series of normal behaviors occupying minutes, hours, days, or weeks and may sense a missing period of time in their experience. In dissociative disorders, the normal integration of consciousness, memory, perceptions, identity, emotion, body representation, motor control, and behavior is disrupted, and continuity of self is lost.
People with a dissociative disorder may experience the following:
Unbidden intrusions into awareness with loss of continuity of experience, including feelings of detachment from self (depersonalization) and/or the surroundings (derealization) and fragmentation of identity
Memory loss for important personal information (dissociative amnesia)
Dissociative disorders frequently develop after overwhelming stress (1). Such stress may be generated by traumatic events or by intolerable inner conflict. Dissociative disorders are related to trauma and stressor-related disorders (acute stress disorder and posttraumatic stress disorder [PTSD]), which can include dissociative symptoms (eg, amnesia, flashbacks, numbing, depersonalization/derealization). A dissociative subtype of PTSD has been established to classify patients who meet all the diagnostic criteria for PTSD but also experience depersonalization, derealization, or both.
Brain research in animals and humans has begun to identify specific brain structures and functions underlying dissociation. In particular, during dissociation rhythmic activity occurs in a deep posteromedial region, including the posterior cingulate cortex, that is disconnected from higher cortical regions responsible for thought and planning (2). Similarly, during hypnosis there is a relative disconnection of those higher control regions from a portion of the back of the brain (the posterior cingulate cortex) that is involved in self-reflection (3). In addition, trauma-related dissociation appears to involve increased activation of the ventromedial prefrontal cortex and decreased connectivity with the cerebellum and orbitofrontal cortex (4).
General references
1. Rafiq S, Campodonico C, Varese F: The relationship between childhood adversities and dissociation in severe mental illness: A meta-analytic review. Psychiatr Scand. 138(6):509-525, 2018. doi: 10.1111/acps.12969
2. Vesuna S, Kauvar IV, Richman E, et al: Deep posteromedial cortical rhythm in dissociation. Nature 586(7827):87-94, 2020. doi: 10.1038/s41586-020-2731-9
3. Jiang H, White MP, Greicius MD, et al: Brain activity and functional connectivity associated with hypnosis. Cereb Cortex 27(8):4083-4093, 2017. doi: 10.1093/cercor/bhw220
4. Lebois LAM, Harnett NG, Rooij SJH, et al: Persistent dissociation and its neural correlates in predicting outcomes after trauma exposure. Am J Psychiatry 179(9):661-671, 2022. doi: 10.1176/appi.ajp.21090911
