- The investigators will adhere to the operational definition of mild TBI suggested by the World Health Organization Task Force (Holm et al 2005), with the exception of Glasgow Coma Scale score criteria (not available for these subjects): a.) One or more of the following: confusion or disorientation, loss of consciousness for 30 minutes or less, post-traumatic amnesia for less than 24 hours, and/or other transient neurological abnormalities such as focal signs, seizure, and intracranial lesion not requiring surgery; Glasgow Coma Scale (GCS) score of 13-15 after 30 minutes post-injury or later upon presentation for health care (GCS unavailable). This WHO diagnostic definition of mild TBI is also consistent with the CDC Report to Congress on Mild TBI in the United States, September 2003 (specifically, altered consciousness attributable to the head injury [=transient confusion, disorientation or impaired consciousness] or self reported loss of consciousness lasting 30 minutes or less).