For some people with post-traumatic stress disorder (PTSD), symptoms go beyond the flashbacks, nightmares, sleeplessness, and tense feelings that trouble many. Up to 30 percent of people with PTSD also suffer from symptoms known as depersonalization and de-realization––that is, they experience “out-of-body” episodes or feelings that the world is not real. These disturbances to awareness and consciousness are known as dissociation.

New research now reveals that brain circuits involved in fear processing are wired differently in these people than in others diagnosed with PTSD. The findings, reported in Neuropsychopharmacology, suggest that such patients need different treatment options.

PTSD with dissociation is recognized as a distinct subtype of the disorder. It is most common among people whose PTSD developed after repeated traumas or childhood adversity. Genetic factors can also increase the risk of developing PTSD with dissociation.

Studies have found that reminders of traumatic events trigger different patterns of neural activity in patients with dissociative PTSD than they do in people who have PTSD without dissociation. In both groups, emotion-regulating brain circuits are thought to be disrupted. Emotional responses are undermodulated (under-regulated, or controlled) by the brain in most people with PTSD, causing them to relive traumatic events and experience hyperarousal symptoms such as being easily startled. In people with the dissociative subtype of PTSD, in contrast, emotional responses are overmodulated (over-regulated) by the brain, leading to emotional detachment and the subtype's characteristic feelings of depersonalization and derealization.

Senior author Ruth Lanius, M.D., Ph.D., of the University of Western Ontario led a team of scientists that included two-time (2007 and 2009) NARSAD Young Investigator grantee Margaret McKinnon, Ph.D., of McMaster University in Ontario. The scientists used functional magnetic resonance imaging to compare activity in the brains of 49 people with PTSD, 13 of whom had been diagnosed with the dissociative subtype of the disorder. Their study also included 40 people without PTSD.

The researchers focused their analysis on parts of the brain that connect to the amygdala, a small structure deep in the brain that is involved in emotion and fear processing. They examined connections to two parts of the amygdala: the basolateral amygdala, which evaluates sensory information and helps integrate emotions, and the centromedial amygdala, which helps execute fear responses.

They found that in the brains of patients with the dissociative subtype of PTSD, the amygdala was more strongly connected to brain regions involved in consciousness, awareness, emotional regulation, and proprioception (the sense of body position) than it was in PTSD patients without the dissociative subtype. The researchers say that patients' dissociative symptoms may be directly related to these alterations in the brain's functional circuitry.

Read the abstract.