Inclusion Criteria:  Volunteers must have a history of mild traumatic brain injury, specifically, persistent post-concussive symptoms after examination by a neuropsychologist or neurologist. Volunteers time from concussive incident (Mild traumatic brain injury) must be between 3 months - 5 years following head trauma incident TBI was caused by non-penetrating trauma Volunteers must have current complaints of TBI symptoms such as headache, dizziness, or cognitive or affective problems Volunteers must be 18-year-old or more Willing and able to provide informed consent Able to speak and read English, as primary language Agrees to provide blood samples for clinical lab tests Willing and committed to comply with research protocol and complete all outcome measures Able to equalize middle ear pressures or willing to undergo needle myringotomies if needed Willingness and committed to comply with study protocol outlined reproductive plan based on baseline reproductive status  Exclusion Criteria:  Prior treatment with hyperbaric oxygen treatment Hyperbaric chamber inside attendant, professional, SCUBA diver (technical, commercial, operational/military or recreational) The investigators will exclude pregnant women from this study because potential fetal adverse reactions triggered by high oxygen partial pressures such as retrolenticular fibroplasia though careful review of human data are generally reassuring such as the use of hyperbaric oxygen to treat acute carbon monoxide poison in the pregnant patient.13 Prisoners Minors Unable to protect airway or requires frequent suctioning Known or suspected peri-lymphatic fistula Presence of tracheostomy (due to limitations in auto-inflating the middle ear) Unable to participate fully in outcome assessments Unable to cooperate with hyperbaric oxygen treatments Unable to speak and read English, as primary language Not cooperating with instructions during hyperbaric oxygen treatments such as bringing contraband items into the chamber (such as fire lighter) Not competent to sign their own consent. Such potential participants will not have the capacity to participate in a full range of neurocognitive testing Pre-existing diagnosis of a psychotic disorder(s): schizophrenia, bipolar, dissociative disorder History of moderate or severe traumatic brain injury History of brain injury not of traumatic etiology such as stroke or drug-induced coma Verifiable diagnosis of learning disability. Other pre-existing cognitive issues may make it difficult for potential participants to fill out certain outcome assessments such as neurobehavioral symptomatic inventory. This could lead to measurement bias or confound the result. Claustrophobia and unwilling to enter hyperbaric chamber Untreated pneumothorax Presence of implanted device with un-verifiable test to pressure by manufacturer Concurrent enrollment in an alternate interventional trial for post concussive symptoms