In this study, individuals will undergo an assessment that includes taking a history of their previous exposure to traumatic events, an assessment of current mental health symptoms including those associated with PTSD, and an assessment of physiologic measures, including ERG as well as vital sign measurements, blood draw, and saliva sampling. Participants will be given a single dose of sertraline (50mg), and a repeat ERG will be administered. An optional open label phase of the study will follow, in which participants who undergo treatment with an antidepressant will be invited back for a follow-up assessment with repeat ERG.