 The purpose of this study is to determine if hyperbaric oxygen therapy HBOT improves the cognitive function of OIFOEF individuals who have chronic mild to moderate traumatic brain injury TBI. Cognitive function includes such things as thinking, remembering, recognition, concentration ability and perception. Traumatic brain injury is common with head injuries caused by blows to the head, nearby explosions, or concussion. Subjects will be assigned to an intervention or sham arm. Computer based cognitive tests will be used as outcome measures. Subjects are enrolled by invitation only. 