The purpose of this study is to determine if clinic and home training with a study device will improve a balance deficit. The study device is called Portable Neuromodulation Stimulator (PoNS). The study device will be placed on the tongue to deliver nerve stimulation. The study is testing if use of the study device in conjunction with physical therapy will improve balance and gait in patients suffering from a TBI. The effects of using the device and undergoing therapy will be measured using standardized tests of movement control, gait, headache and other TBI symptoms.

Inclusion Criteria:

• Male or female, 18-65 years of age
• Documentation on initial TBI (defined as closed-head, non-penetrating, blunt, whiplash, or explosive blast-induced brain injury) severity (at time of injury): Glasgow Coma Scale (GCS) score 9-15, with loss of consciousness < 24 hours, post-traumatic amnesia ≤7 days, or hospital admission ≤ 7 days post TBI
• If female, subject is not pregnant, not lactating, has a negative pregnancy test prior to receipt of the PoNS™ device, and agrees to use contraception from screening to end of the study
• Balance disorder with SOT composite score at least 16 points below normal resulting from a mild/moderate TBI without any concomitant pathologies
• At least 1 year post injury
• Stable neurologic status
• Prior participation in a focused physical rehabilitation program for TBI and deemed by their treating clinician/themselves to have reached a plateau
• Able to walk continuously on a treadmill for 20 minutes, level grade and at any speed, with support if needed
• Access to a treadmill and commitment to utilize this for the at-home portion of the study
• Able to understand the study procedures and give informed consent
• Willing and able to adhere to the study schedule
• Willing to complete a neuropsychological evaluation prior to inclusion

Exclusion Criteria:

• Medical finding from screening history and physical examination that is clinically significant or would otherwise impact patient safety or data integrity
• Medical finding from prior neuroradiologic study or recent MRI that is significant or that would impact patient safety or data integrity
• Planned use or use of any investigational product, pharmaceutical or device within 30 days preceding receipt of the PoNS device and during the entire study
• Balance or gait deficits due to lower extremity injury or neurological condition other than TBI
• Penetrating brain injury, craniotomy or refractory subdural hematoma
• Oral health problems at the time of recruitment
• Oral surgery within 3 months of screening
• History of oral cancer
• Non-removable metal orthodontic devices that could interfere with PoNS use
• Presence of metallic implant or other MRI-incompatible device
• Blood pressure abnormalities considered clinically significant
• Use of Coumadin or other anticoagulant except aspirin in the last 6 months
• Untreated or undiagnosed diabetes
• Diabetic neuropathy
• Active or recent (within 1 year) treatment for any cancer, excluding basal cell carcinoma.
• Neurological disorders other than those attributed to the primary diagnosis (neurodegenerative diseases such as Multiple Sclerosis, Parkinson's disease, Alzheimer's disease or other dementia, Amyotrophic Lateral Sclerosis)
• History of epileptic or other seizure disorders
• Known ischemic heart disease and/or history or atrial or ventricular arrhythmias with or without syncope
• Any other untreated or unstable acute or chronic, clinically significant medical condition for which the subject is currently undergoing treatment that the study investigator deems unsuitable for inclusion
• Use of a lower extremity biomechanical prosthetic with the exception of a splint for foot drop
• Females who are pregnant, lactating, or planning to become pregnant during the study
• Chronic use of any potentially interfering medication, or use of any medication that would compromise the ability to function or perform the study activities
• Addition of and/or major change in type or dosage of any prescription medication within 3 months prior to receipt of the PoNS device
• Active alcoholism. The study investigator will have the right to exclude subject participation if the subject seems intoxicated at time of screening and/or during any study appointment.
• History of drug abuse will be assessed
• Recent history of smokeless tobacco use
• Any reason that may be a threat to health or safety
• Any finding in the neuropsychological evaluation that makes the subject unsuitable for inclusion