Background: Posttraumatic stress disorder (PTSD) has been most consistently associated with exaggerated physiologic reactivity to startling sounds when such sounds occur in threatening contexts. There is conflicting evidence about whether startle hyperreactivity is a preexisting vulnerability factor for PTSD or an acquired result of posttrauma neural sensitization. Until now, there have been no prospective studies of physiologic reactivity to startling sounds in threatening contexts as predictors of PTSD symptoms.
Methods: One hundred and thirty-eight police academy cadets without current psychopathology were exposed to repeated 106-dB startling sounds under increasing (low, medium, or high) threat of mild electric shock while their eye-blink electromyogram, skin conductance, heart rate, and subjective fear responses were recorded. Measures of response habituation were also calculated. Following 1 year of exposure to police-related trauma, these participants were assessed for PTSD symptom severity.
Results: After accounting for other baseline variables that were predictive of PTSD symptom severity (age and general psychiatric distress), more severe PTSD symptoms were prospectively and independently predicted by the following startle measures: greater subjective fear under low threat, greater skin conductance under high threat, and slower skin conductance habituation.
Conclusions: These results imply that hypersensitivity to contextual threat (indexed by greater fear under low threat), elevated sympathetic nervous system reactivity to explicit threat (indexed by larger responses under high threat), and failure to adapt to repeated aversive stimuli (evidenced by slower habituation) are all unique preexisting vulnerability factors for greater PTSD symptom severity following traumatic stress exposure. These measures may eventually prove useful for preventing PTSD.