Motoneuron Recruitment and Motor Evoked Potential Up-Conditioning (MEP) in Spinal Cord Injury (SCI)

Inclusion Criteria: * Adult (≥18 yrs old) * a history of injury to spinal cord at or above C6 * neurologically stable (\>1 year post SCI) * medical clearance to participate * weak wrist extension at least unilaterally * expectation that current medication will be maintained without change for at least 3 months. * Stable use of anti-spasticity medication (e.g., baclofen, diazepam, tizanidine) is accepted. (Because only neurologically stable subjects will enter this study, medication changes will be unlikely.) * In participants with bilateral wrist extension weakness in whom Extensor Carpi Radialis (ECR) MEP can be elicited in both arms, the more severely impaired arm is studied. In participants with unilateral wrist weakness or in participants with bilateral wrist weakness in whom an ECR MEP can be elicited in only one arm, that arm is studied. Exclusion Criteria: * motoneuron injury * unstable medical condition * cognitive impairment (because the studied intervention is a learning-based intervention) * a history of epileptic seizures * a pre-existing or confounding neurological condition (e.g., history of MS, Stroke, Parkinson's disease) * metal implants in the cranium * implanted biomedical device in or above the chest (e.g., a cardiac pacemaker, cochlear implant) * no measurable MEP elicited in the ECR * inability to produce any voluntary ECR EMG activity * extensive use of functional electrical stimulation to the arm on a daily basis (as it may interfere with or augment the effects of MEP conditioning itself) * pregnancy (due to changes in posture and potential medical instability) * inability or unwillingness of subject or legal guardian/representative to give informed consent