(PSYCHIATRIC TIMES) - Dissociation—a common feature of posttraumatic stress disorder (PTSD)1,2—involves disruptions in the usually integrated functions of consciousness, memory, identity, and perception of the self and the environment.3 Acute dissociative responses to psychological trauma have been found to predict the development of chronic PTSD.4-9 Moreover, a chronic pattern of dissociation in response to reminders of the original trauma and minor stressors has been found to develop in persons who experience acute dissociative responses to psychological trauma.9
Bremner and associates10 hypothesized that there may be 2 subtypes of acute trauma response that represent unique pathways to chronic stress-related psychopathology: one is primarily dissociative and the other is predominantly intrusive and hyperaroused. Using data from our own neuroimaging studies,11-16 we will show that these 2 subtypes of response can persist in persons with chronic PTSD17 and that they are associated with distinct patterns of neural activation upon exposure to reminders of traumatic events.
The term “dissociation” has denoted a wide variety of phenomena in the literature encompassing both states and traits. Here the focus is on dissociative symptomatic responses to trauma-related stimuli in PTSD—particularly states of depersonalization and derealization. We have operationalized this definition with 4 questions from the Responses to Script-Driven Imagery Scale, which is a validated measure of evoked symptoms that we developed to advance psychobiological and treatment outcome research in PTSD.18
• Did what you were experiencing seem unreal to you, like you were in a dream or watching a movie or play?
• Did you feel like you were a spectator watching what was happening to you, like an observer or outsider?
• Did you feel disconnected from your body?
• Did you feel like you were in a fog?
For most clinicians, these are familiar descriptions of some of their PTSD patients’ responses to trauma-related stimuli and situations, and such states are witnessed firsthand in their offices.
Functional brain imaging studies
Over the past 15 years, the application of functional neuroimaging research on PTSD has resulted in an explosion of new data that have begun to reveal the brain circuits that are involved in the pathophysiology of this disorder. Studies that use positron emission tomography (PET) and blood oxygenation level–dependent functional MRI (BOLD fMRI) have examined neural responses to a variety of stimuli, including fearful, happy, and neutral faces; trauma-related images and sounds; and “script-driven imagery” of traumatic experiences. A recent review and meta-analysis found that persons with PTSD tend to exhibit greater brain activation in the amygdala and insula than persons without PTSD; these structures are involved in fear conditioning and the perception of bodily states (among other functions), respectively.19 Moreover, the dorsal anterior cingulate cortex (ACC), rostral ACC and ventromedial prefrontal cortex, which are involved in the experience and regulation of emotion, have repeatedly been observed to be less activated in patients with PTSD than in controls who have a history of trauma but not PTSD.19
Our research has shown that in patients with PTSD, psychobiological responses to recalling traumatic experiences can differ significantly, and a sizable proportion do not fit the conventionally studied “reexperiencing/hyperaroused” response.20,21 For example, in our initial brain imaging studies, approximately 70% of patients relived their traumatic experience and showed an increase in heart rate while recalling the traumatic memory,11,13 while the other 30% had a dissociative response with no concomitant increase in heart rate.14,15
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