Hyperbaric Oxygen for Traumatic and Non-traumatic Brain Injury

Inclusion Criteria: * Adults, age 18-70 years, both men and women * Able to speak and read English as primary language * Able and willing to provide written informed consent for study participation. * Able and willing to complete outcome assessments and provide blood and urine samples as required by the study protocol. * Able to tolerate the chamber environment and hood placement and to equalize middle ear pressure. * Past history of at least one brain injury with persistent symptoms that meets all of the following criteria: * Brain injury of non-stroke etiology that occurred at least 6 months but no more than 10 years prior to enrollment. * At least 3 of the following persistent symptoms from the injury: headaches, dizziness or balance problems, blurred vision, tiredness/fatigue or sleep problems, seizures, remembering things or solving problems, managing stress or emotional upsets, controlling temper/irritability, depression, anxiety, post-traumatic stress, or ringing in the ears. * Normal thyroid stimulating hormone and hematocrit value greater than 35% within the previous 6 months. Exclusion Criteria: * Contraindications to hyperbaric oxygen * Insulin-dependent diabetes mellitus, or diabetes mellitus that is not reasonably controlled. * Uncontrolled seizure disorder (participants must be on therapy and seizure-free for at least 6 months). * Claustrophobia precluding chamber or hood tolerance. * Implanted devices not cleared for hyperbaric pressurization. * Pregnancy or plans to become pregnant during the study participation period. Women of childbearing potential will be asked to use an acceptable form of birth control during study participation. * Lung disease, such as emphysema, chronic bronchitis, asthma that is not well-controlled, or bullous lung disease that raises the risk for pulmonary barotrauma due to air trapping. * Active malignancy, previous malignancy (except basal cell carcinoma) in the last 5 years, or any prior treatment with bleomycin (Blenoxane). Prior treatment with doxorubicin (Adriamycin) is acceptable as long follow-up echocardiography is normal. * Chronic disease such as heart or renal failure would raise the participant's risk of adverse events during hyperbaric oxygen. * Confounds to the outcome assessments * Inability to speak English as their primary language (English fluency required because many of the outcomes are only in available in English) * Instability with walking requiring more than a cane for assistance * Alcohol abuse, by self-report, within the last year. * Lifetime history of illicit drug use, by self-report, except remote (greater than one year), non-habitual use of marijuana. * Failed urine drug screen during study participation. * Continued participation during the intervention period in sports activities where head injury is likely, such as contact football, boxing, mixed martial arts, etc. * Blind or deaf. * Major psychiatric disorder or degenerative mental disease (such as multiple sclerosis). * Prior therapeutic radiation to the central nervous system. * Personal history of any condition that pre-dates their brain injury that resulted in diminished capacity (such as chromosomal disorders) or that, in the opinion of the investigators, affects cognition to such a degree that the outcome assessments are invalidated (such as learning disability or attention deficit hyperactivity disorder requiring pharmaceutical therapy as an adult). * Any brain injury from stroke (ischemic or hemorrhagic) * Known untreated chronic or acute medical conditions, such as hypothyroidism, Cushing's disease, untreated hypertension, etc., that would confound the outcome assessments or inhibit compliance with the study protocol. If treated, these disorders would not be excluded. * Concomitant enrollment in any other drug/device clinical trial. * Prior hyperbaric oxygen for any reason within the last year.