engleski

Conditioned and external fear inhibition in combat- related PTSD in Croatian war veterans.

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. In the present study we used the same conditioned inhibition experiment with fear-potentiated startle (AX+/BX-) in 33 human subjects from Croatia (16 controls and 17 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. Subjects indicated trial-by-trial airblast expectancy by pressing buttons on a keypad. The controls showed more fear-potentiated startle in the presence of AX+ than BX- (F(1, 15)=11.59, p<0.001) ; and inhibited potentiation to AB compared to AX+ (F(1, 15)=7.61, p=0.01). Startle to AC was not inhibited relative to AX suggesting that pre-exposure eliminated external inhibition. Furthermore, in the controls, AB was inhibited relative to AC (F(1, 15)=6.17, p<0.05) showing transfer of safety. The PTSD patients did not show discrimination compared to AX+ on either AB or AC, and hence did not transfer safety to the AB trial. The expectancy ratings showed that both the control and PTSD subjects did not expect an airblast on the AB or AC trials ; however, only the controls showed inhibition of startle on the AB trials. 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.

PTSD; posttraumatic stress disorder; fear; war veterans

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