Several lines of evidence suggest that PTSD symptoms are mediated by dysfunctional processes involving the brain's fear-circuitry network in general, and extinction learning and recall deficits in particular. Based on our preliminary work in applying fear extinction task to healthy humans and patients with PTSD the goal of this renewal RO1 application is to employ an established extinction paradigm with functional magnetic resonance imaging (fMRI) and Skin Conductance Response (SCR) assessments in a large and well characterized sample with PTSD and trauma exposed healthy control (TE-HC) subjects. We plan to clarify circuits underlying PTSD psychopathology and to probe, for the first time, neural circuitry of symptomatic improvement in response to Prolonged Exposure (PE) treatment. This goal is congruent with NIMH strategic plan strategy 1.3 ("identify and integrate biological markers and behavioral indicators associated with mental disorders").