The aims above will be accomplished through four years of study, conducted by a multi-disciplinary research team, comprised of research scientists from Columbia, Harvard and New York Universities, who have conducted studies in PTSD and structural and functional brain imaging. If successful, the study will produce highly needed information on the neural circuitry which underlies deficient extinction and recall in PTSD, and will provide highly important information about the neural effects of Prolonged Exposure treatment, a first line treatment for PTSD. Together these lines of expected findings will not only advance identification of biomarkers associated with PTSD, but also facilitate identification of biomarkers for clinical reponse to an empirically supported treatment.