EFFECT OF DARKNESS ON ACOUSTIC STARTLE IN VIETNAM VETERANS WITH PTSD

Objective: Exaggerated startle is a symptom of posttraumatic stress di sorder (PTSD), but empirical studies have not consistently documented elevated baseline startle in PTSD. The authors proposed in a previous study that Vietnam veterans with PTSD exhibit exaggerated startle only under stressful conditions, They reported that darkness facilitated s tartle in humans, suggesting that the startle reflex is sensitive to t he aversive nature of darkness. In the present study they tested the h ypothesis that the magnitude of facilitation of startle by darkness wo uld be greater in Vietnam veterans with PTSD than in comparison groups of subjects without PTSD. Prepulse inhibition was also investigated. Method: The magnitude of startle and prepulse inhibition were assessed in alternating periods of darkness and light in 19 non-medicated Viet nam veterans with PTSD, 13 Vietnam veterans without PTSD, and 20 civil ians without PTSD. Results: The overall startle level was higher in th e veterans with PTSD than in either of the two groups of subjects with out PTSD. Startle runs facilitated by darkness, and the magnitude of t his facilitation was greater in the veterans with PTSD than in the civ ilians without PTSD, but it was not greater in the veterans without PT SD. Prepulse inhibition was not affected by darkness and did not signi ficantly differ among groups. Conclusions: Contrary to the hypothesis, elevated sensitivity to darkness was specific to individuals with com bat experience, not to individuals with PTSD, perhaps because veterans had become aversively conditioned to darkness during their combat exp eriences. The more general increase in startle reactivity in the veter ans with PTSD is consistent with clinical observations and description s of symptoms in DSM-IV.