Posttraumatic stress disorder may be associated with impaired fear inhibition: relation to symptom severity

Abstract

One of the central problems in posttraumatic stress disorder (PTSD) is the inability to suppress fear even under safe conditions. The neural underpinnings of fear are clinically relevant but poorly understood. This study assessed fear potentiation and fear inhibition using fear-potentiated startle in a conditional discrimination procedure (AX+/BX-). We hypothesized that patients with PTSD would show normal fear potentiation and impaired fear inhibition. Subjects comprised 28 healthy volunteers and 27 PTSD patients (14 with low current symptoms, 13 with high current symptoms) who were presented with one set of colored lights (AX trials) paired with aversive air blasts to the throat, and a different series of lights (BX trials) presented without air blasts. We then presented A and B together (AB trials) to see whether B would inhibit fear potentiation to A. All groups showed robust fear potentiation in that they had significantly greater startle magnitude on AX trials than on noise-alone trials. However, the high-symptom PTSD group did not show fear inhibition: these subjects had significantly greater fear potentiation on the AB trials than both the controls and the low-symptom PTSD patients.

Figure 1

Diagram of the AX+/BX-startle session.

Figure 2

Startle amplitude (mean + SEM) to noise alone (NA) and in the presence of the reinforced stimulus (AX+) in controls, low symptom, and high symptom PTSD subjects. Brackets indicate significant contrasts. *P<0.05. **P<0.01.

Figure 3

Percent potentiation (mean + SEM) from noise alone to AX+, BX-, AB, and AC trial types in control, low symptom, and high symptom PTSD subjects. Brackets indicate significant contrasts. *P<0.05. **P<0.01. †P<0.1

Figure 4

Expectancy ratings (mean + SEM) for AX+, BX-, AB, and AC trial types in low symptom and high symptom PTSD subjects. Positive score indicate airblast expectancy, negative scores indicate that there is no expectancy of airblast, and zero indicates uncertainty. Brackets indicate significant contrasts. **P<0.01.