engleski

Impaired inhibition of fear in combat-related PTSD: replication and extension

Background: One of the central problems in posttraumatic stress disorder (PTSD) is impaired fear inhibition under safe conditions. Our previous studies showed that patients with the highest symptoms have impaired inhibition of fear-potentiated startle. However, this impairment was seen both in conditioned inhibition (in the presence of a safety signal) and in external inhibition (in the presence of a novel stimulus), both of which were present in the controls. Methods: We used a conditional discrimination procedure (AX+/BX-) with a human fear-potentiated startle paradigm in 55 human subjects from Croatia (22 controls and 33 PTSD patients). In this paradigm one set of stimuli (AX+) predicted an aversive air blast and another set of stimuli (BX-) predicted omission of the air blast. The AB compound trial measured conditioned inhibition in which B transferred inhibition to A, while the AC trial measured external inhibition since C is neutral. Prior to the AX+/BX- session all subjects were given a pre-exposure session to all stimuli in order to reduce the effect of novelty. Results: The controls showed more fear-potentiated startle in the presence of AX+ than BX- (F(1, 21)=19.06, p<0.001) ; and inhibited potentiation to AB compared to AX+ (F(1, 21)=12.28, p<0.005). Startle to AC was not inhibited relative to AX+. The PTSD patients showed discrimination between AX+ and BX- (F(1, 32)=4.61, p<0.05) ; However, neither AB nor AC were inhibited relative to AX+. Conclusions: These results suggest that impaired inhibition of fear-potentiated startle in PTSD patients is specific to conditioned inhibition, i.e., that they cannot transfer inhibition from a safety signal. Support: This research was supported by the Croatian Ministry of Science, Education and Sport project: Integrative diagnostical model for the stress-related disorders (PI, D. Kozaric-Kovacic), and the National Institutes of Mental Health Kirschstein National Research Service Award Individual Fellowship 1F32 MH070129-01A2 (PI, T. Jovanovic).

inhibition; fear; PTSD; posttraumatic stress disorder

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