Elsevier

Biological Psychiatry

Volume 66, Issue 1, 1 July 2009, Pages 47-53
Biological Psychiatry

Archival Report
Increased Anxiety During Anticipation of Unpredictable Aversive Stimuli in Posttraumatic Stress Disorder but not in Generalized Anxiety Disorder

https://doi.org/10.1016/j.biopsych.2008.12.028Get rights and content

Background

Uncontrollability and unpredictability are key concepts related to re-experiencing, avoidance, and hypervigilance symptoms of posttraumatic stress disorder (PTSD). However, little is known about the differential sensitivity of PTSD individuals to unpredictable stressors, relative to either healthy individuals or individuals with other anxiety disorders. This study tested the hypothesis that elevated anxious reactivity, specifically for unpredictable aversive events, is a psychophysiological correlate of PTSD.

Methods

Sixteen patients with PTSD (34.5 ± 12.4 years) were compared with 18 patients with generalized anxiety disorder (GAD) (34.0 ± 10.5 years) and 34 healthy control subjects (30.2 ± 8.5 years). Participants were exposed to three conditions: one in which predictable aversive stimuli were signaled by a cue, a second in which aversive stimuli were administered unpredictably, and a third in which no aversive stimuli were anticipated. Startle magnitude was used to assess anxious responses to the threat cue and to contexts associated with each condition.

Results

Posttraumatic stress disorder and GAD patients showed normative enhancement of fear to the predictable threat cue, but the PTSD group displayed elevated anxiety during the unpredictable condition compared with participants with GAD and healthy control subjects.

Conclusions

Anxious reactivity to unpredictable aversive events was heightened in PTSD but not in GAD and healthy subjects. Prior works also found signs of increased reactivity to unpredictable threat in panic disorder (PD), suggesting that PTSD and PD may involve shared vulnerability. As such, the current results inform understandings of classification, pathophysiology, and psychopharmacology of anxiety disorders, generally, and PTSD and panic disorder specifically.

Section snippets

Participants

Sixteen medication-free PTSD patients (9 women and 7 men; mean ± SD age, 34.5 ± 12.4 years), 18 GAD patients (14 women and 4 men; mean ± SD age, 34.0 ± 10.5 years), and 34 healthy control subjects (25 women and 9 men; mean ± SD age, 30.2 ± 8.5 years) participated in the study. Mean age did not significantly differ across groups [F(1,62) = .9, ns). The patients met DSM-IV criteria for PTSD or GAD as assessed by the Structural Clinical Interview for DSM-IV Axis I Disorders (SCID-I) (21).

Startle Magnitude

Startle data (raw and T scores) are presented in Table 1. Overall startle magnitudes (raw scores) appear larger in the PTSD group compared with the other groups, but this effect was not significant [omnibus ANOVA (group [3] × condition [2] × cue [cue, no cue]): F(2,62) = 1.6, ns].

Discussion

As hypothesized, PTSD patients compared with GAD patients and healthy control subjects displayed heightened anxiety during periods of unpredictable, but not predictable, threat. Specifically, startle potentiation during the no-cue period of the unpredictable versus neutral condition—reflecting heightened contextual anxiety—was observed only in the PTSD group. In contrast, fear-potentiated startle to the threat cue predictably signaling the aversive events was increased to the same extent in the

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