Cortical Plasticity Assessment in Athletes With a History of Concussion

Inclusion Criteria: * Student-athletes at risk for traumatic brain injury (collegiate football, ice hockey) * Age between 18 and 30 yr. * Concussion as defined by the American Academy of Neurology: trauma-induced alteration in mental status that may or may not involve loss of consciousness (confusion and amnesia are the hallmarks of concussion) * Concussion that occurred \> 6 months * All head injuries classified as minor with a Glasgow Coma Scale of 13 to 15 at the time of the trauma * Participants are cleared for full sport participation based upon neurological and neuropsychological (NS) assessments Classified as symptomatic based on Post-concussion Symptom List Exclusion Criteria: * Previous significant neurological history * Use of tricyclic anti-depressants such as amitriptyline, nortriptyline and imipramine within the past six months. * Use of anticonvulsants such as carbamazepine, phenytoin, valproic acid and gabapentin within the past six months * History of seizures, depression or PTSD * Presence of post-concussion symptoms such as complaints of loss of concentration, dizziness, fatigue, headache, irritability, visual disturbances, and light sensitivity. * Contraindications to single pulse TMS (TMS will be used to measure cortical excitability) such as metal head implants * history of seizures * unexplained loss of consciousness * metal in the head * frequent or severe headaches or neck pain * implanted brain medical devices. * Contraindications to tDCS: * metal in the head * implanted brain medical devices For the control group (subjects with no concussion) we will select subjects according to the previously stated list of exclusions as well as the following criteria: Subjects who are athletes (similar to the concussed group) with the same age range and also similar level of education; however these subjects will have no prior history of concussion or neurological insult as self reported. They should also have no contraindications to TMS or tDCS.