Prior studies highlight how threat-related arousal may impair hippocampal function. Hippocampal impairments are reliably associated with post-traumatic stress disorder (PTSD); however, little research has characterized how increased threat-sensitivity may drive arousal responses to alter hippocampal reactivity, and further how these alterations relate to the sequelae of trauma-related symptoms. In a sample of individuals recently exposed to trauma (N=117, 76 Female), we found that PTSD symptoms at 2-weeks and 3-months were associated with decreased hippocampal responses to threat as assessed with functional magnetic resonance imaging (fMRI). Further, decreased hippocampal threat sensitivity was predicted by individual differences in fear-potentiated startle, an arousal-mediated behavior. Critically, the relationship between hippocampal threat sensitivity and PTSD symptomology only emerged in individuals who showed high threat-related arousal. Collectively, our finding suggests that development of PTSD is associated with threat-related decreases in hippocampal function, due to increases in fear-potentiated arousal.

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