Effects of experimental context and explicit threat cues on acoustic startle in Vietnam veterans with posttraumatic stress disorder.

BACKGROUND The hypothesis that exaggerated startle in Vietnam veterans with posttraumatic stress disorder (PTSD) reflects an anxiogenic response to stressful contexts was tested. METHODS Thirty-four nonmedicated Vietnam veterans with PTSD, and 17 combat and 14 civilian non-PTSD controls participated in two testing sessions over separate days. Acoustic startle stimuli were delivered alone or in a test of prepulse inhibition. In the first session, startle was assessed without experimental stress. In the second session, startle was investigated during a stressful "threat of shock" experiment, when subjects anticipated the administration of shocks during threat periods and during safe periods when no shocks were anticipated. RESULTS The magnitude of startle did not differ significantly among the three groups in the first session, but was increased throughout the threat of shock experiment in the PTSD veterans in the second session. The actual increase in startle in the threat compared to the safe condition did not significantly differ among the three groups. Prepulse inhibition was reduced in the PTSD veterans, compared to the non-PTSD civilians, but not compared to the non-PTSD veterans. CONCLUSION Exaggerated startle in Vietnam veterans with PTSD reflects an anxiogenic response to an environment that is experienced as stressful.