One hundred subjects including 60 individuals with a principal diagnosis of PTSD and 40 trauma exposed healthy controls will be assessed by fMRI and SCR to determine the neural circuitry activation to the fear extinction task. fMRI data will be acquired simultaneously with fear extinction and recall measurement quantified by SCR. All 60 PTSD subjects and 20 randomly assigned TE-HCs subjects will repeat these procedures 10 weeks later, after PTSD subjects have completed 10 weeks of intensive PE treatment. Three months after treatment completion clinical ratings of PTSD severity will be conducted to permit analysis of neural predictors of long term treatment durability.