The Warfighter Head Injury Study (WHIS) is a comprehensive, multidisciplinary research study of head-injured warfighters to be conducted at the National Institutes of Health (NIH) in Bethesda, Maryland. The goals of the WHIS include providing clinicians and scientists with new insights into the short term recovery of function following traumatic brain injury (TBI), the role of the prefrontal cortex (PFC) in executive and social functions, and to identify better predictors of short term outcome (including cognitive, neurological, and genetic factors). With the assistance of the Department of Veterans Affairs/Veterans Health Administration (VA/VHA), we propose to contact all Iraqi-Afghan (IA) warfighters with penetrating head injury (PHI), a cohort of blast injured warfighters, and a group of matched (for time in service, combat exposure, age, gender, and preinjury Armed Services Vocational Aptitude Battery [ASVAB] scores) healthy warfighter controls as well as healthy volunteers with different blast exposures (i.e.: explosives experts, artillery operators, etc ) but no documentation of brain injury. We will inquire about their willingness to participate in a comprehensive, multidisciplinary outpatient evaluation conducted at the NIH. In addition to IA warfighters, we also plan to enroll Vietnam warfighters who were included in the W. F. Caveness Vietnam Head Injury Study (VHIS) Registry, in order to conduct detailed comparisons between groups. These cohorts represent a unique opportunity for study; they were healthy and employed before injury, preinjury intelligence testing is available, and the VA/VHA permits long-term follow-up. We have previously investigated Vietnam warfighters with PHI and the published results of those studies have changed the management and evaluation of head-injured warfighters, and contributed to knowledge of brain function and the long-term effects of head injury. Furthermore, based on the knowledge acquired in our previous research with Vietnam warfighters and our current interests in the functions of the human PFC, cognitive neuroplasticity in the young brain, posttraumatic stress disorder (PTSD), posttraumatic epilepsy (PTE), caregiver stress, and genetic-plasticity relationships, we are proposing a series of new cognitive neuroscience experiments and battery of standardized neuropsychological testing to be conducted during the WHIS. In this effort, the experimental testing will be complemented with structural imaging (magnetic resonance imaging [MRI] or computed tomography [CT]), diffusion tensor and perfusion imaging, electroencephalogram (EEG), near-infrared spectroscopy (NIRS), and molecular genetics evaluations. This combination of unique patients, cutting edge cognitive neuroscience experiments and state of the art techniques will lead to new scientific knowledge and improved clinical management of warfighters with TBI.