The tortured brain : Imaging neural representations of traumatic stress experiences using RSVP with affective pictorial stimuli

Abstract

Traumatic stressors such as water boarding, electric shock, or false execution all activate similar bodily, affective, and cognitive responses even when they are quite different from one another. As a result, the memory traces merge into a "trauma network" that includes sensory memories but becomes detached from the particular episodic memory; that is, the trauma network has no time or place. As, with increasing traumatic experiences, more and more cues become integrated in the network, the threshold for excitation is continually lowered and the individual is likely to show frequent alarm and other defense responses to reminders of the trauma. Neuroplastic mechanisms determine subsequent reorganization of brain circuitry in order to adapt to a presumed permanent need for defense. We hypothesized that aversive pictorial material is differentially processed in visual as well as frontal and limbic areas of the traumatized brain. We used Rapid Serial Visual Presentation (three pictures per second) to present aversive, neutral, and appetitive pictorial stimuli. Event-related magnetic fields were recorded in 41 survivors of torture and organized violence who suffered from posttraumatic stress disorder (PTSD) as well as 43 controls with a comparable ethnic background. Traumatized individuals showed an early shift in the processing of aversive pictures from sensory visual areas to fronto-temporal areas and the amygdala compared to controls without trauma-related symptoms. For survivors, as opposed to controls, these stimuli automatically activate aspects of the defense cascade and thus lead to an excitation of action-related neural activity. We conclude that an enlarged fear network in survivors of organized violence has a low excitation threshold, thus leading to prominent PTSD symptoms. A disintegration of the fear network by reconnecting its elements to the respective episodic memory or by some form of inhibition of the network may bring relief.