Conditioned Fear Extinction and Generalization in Posttraumatic Stress Disorder

摘要

Post-traumatic stress disorder (PTSD) can affect an individual following exposure to a traumatic event. The exposure to trauma can evoke intense physical and emotional responses. Psychophysiological symptoms of PTSD can include an enhanced startle response; an effect that may result from an inability to inhibit fear. Conditioned fear can be measured using paradigms such as fear conditioning and fear extinction. Fear-potentiated startle is the process by which an individual s acoustic startle response is enhanced upon presentation of a conditioned stimulus (e.g., a colored shape) that was paired with an unpleasant unconditioned stimulus (e.g., an aversive airblast to the throat). We have analyzed fear-processing in PTSD patients from recent conflicts in the Middle East and healthy volunteers. One colored shape served as the reinforced conditioned stimulus (CS+, danger) and another colored shape served as the nonreinforced condition stimulus (CS-, safety). A 140 p.s.i airblast to the throat was used as the unconditioned stimulus. Subjects were fear-conditioned and, after a 10 minute interval, the subjects were trained to extinguish the fear. PTSD patients from the OIF theaters displayed greater fear- potentiated startle to the safety cue as well as delayed extinction of fear- potentiated startle in comparison to the healthy volunteers. In addition, we have observed a dissociation between physiological levels of fear and cognitive awareness of danger and safety in PTSD patients.