 Study Design: In May of 2007 over 2650 Minnesota National Guard troops of the 134 BCT completed a within-theatre survey on health, exposure to blast, and traumatic events. Fifty-one percent of surveyed troops reported being close enough to an explosive blast that they felt a heat or pressure wave, had trouble hearing, or had subsequent problems with attention or memory. The proposed study will be carried out over a four-year period and include a total of 180 subjects. To determine the neural consequences of blast exposure we will compare the functional and structural brain characteristics of individuals from the 134 BCT who have blast injury, blast injury and PTSD, PTSD, and no blast injury or PTSD. There will be 45 demographically similar subjects in each group. 