| Summary: | Rationale: Post-traumatic stress disorder (PTSD) is associated with exaggerated autonomic responses to sudden, loud acoustic stimuli, particularly under conditions characterized by ambiguous threat. However, it is not clear if such exaggerated responses are a stable vulnerability factor for developing PTSD or a feature of current PTSD that resolves with symptom resolution. We investigated this issue by comparing autonomic startle responses to acoustic stimuli under low, medium, and high threat conditions in Gulf War Veterans with and without current and past PTSD. Methods: Our sample included three groups: no PTSD (n=151), PTSD in remission (n=51), and current PTSD (n=54) (M age = 44.3, SD = 9.6; 11.6% female). Current and past PTSD symptoms were assessed with the clinician-administered PTSD scale. All participants were exposed to an acoustic stimulus in three conditions: 1) low threat, in which participants experienced no threat of shock; 2) medium threat, in which participants wore a finger electrode but were told that they would not get shocked; and 3) high threat, in which participants wore a finger electrode and were told that they would get shocked. Independent sample t-tests were used to compare group differences in startle responding. Results: Individuals with current PTSD had significantly higher heart rate responses compared with the no PTSD group in the low, t(196) = 2.52, p=0.011, and medium threat conditions, t(66.7) = 2.40, p=0.022, and compared with the PTSD in remission group in the low, t(87) =1.957, p=0.05), and medium threat conditions, t(77.81) = 2.50, p=0.02. In analyses, including only patients with current or past PTSD who had current clinician administered PTSD scale (CAPS) across the entire range from 0 to 108 (M = 41.0, SD = 25.4), we found that higher severity of current PTSD symptoms was not only associated with higher startle responses, particularly in the medium threat condition (r = 0.22, p=0.04), but also with trend level in the low (r=0.18, p=.09) and high (r=0.18, p=0.09) threat conditions. Conclusion: These results suggest that exaggerated autonomic startle responses under conditions of low and medium threat vary as a function of current PTSD severity and are not a marker of PTSD vulnerability. Moreover, the data suggest that this startle paradigm with varying threat levels may be a useful index of hyperarousal of fear-related neurocircuitry in PTSD.
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