Optimizing Cortical Priming

Each year over 795,000 people suffer from stroke resulting in the primary cause of adult disability. Persistent upper limb dysfunction due to stroke significantly impairs performance and results in a serious decline of quality of life. As most daily activities involve the use of both arms, restoring the coordination between upper limbs is essential for regaining functional independence. Only a few interventions have been designed for improving function of both arms, and most of these interventions have focused on movement retraining without directly facilitating the injured brain. The purpose of this study is to design and test a noninvasive brain stimulation protocol tailored to enhance the coordination between the arms in individuals with chronic stroke. The investigators propose that the dorsal premotor cortex on the noninjured side of the brain (cPMd) could serve as a potential stimulation target for enhancing arm coordination and brain function. In the first part of this study (Aim 1), the investigators will examine its effects on modulating arm movements in individuals with chronic stroke. In the second part of this study (Aim 2), the investigators will upregulate the activity of the most responsive region (cPMd or iM1) of each participant prior to arm movement training (bilateral arm training, BAT) to determine the combined effects on augmenting bilateral arm coordination and brain function in individuals with chronic stroke.

Inclusion Criteria: Stroke Participants: * Age 50 years and older * Unilateral ischemic cortical or white matter subcortical stroke * At least 6 months post-stroke and have completed all inpatient and outpatient therapy * Residual arm paresis as indicated by Fugl-Meyer Assessment of the Upper Extremity (FMA-UE) scores between 25 and 65 (individuals in this range have demonstrated the ability to generate motor evoked potentials during active muscle contraction) * Able to reach forward for at least 15 centimeters Healthy Controls: * Age-matched to a stroke participant within plus or minus 3 years * Gender-matched to a stroke participant Exclusion Criteria: Stroke Participants and Healthy Controls: * A non-stroke neuromuscular disorder restricting exercise * Stroke involving the brainstem or cerebellum * Any medical conditions that could limit physical activity levels required for testing and training, such as acute cardiac or pulmonary/respiratory conditions, or uncontrolled hypertension (blood pressure greater than 180/100 mmHg) * Significant orthopedic or chronic pain conditions limiting upper extremity movements * Any medications that may adversely impact upper extremity control * Metallic implant in the head or chest, implanted pumps/stimulators/shunts, or cardiac pacemaker * A history of seizures * Use of any neuropsychoactive medication * History of fainting spells of undetermined etiology * Pregnancy * Any other concomitant neurological condition affecting sensorimotor systems, such as brain tumor, substance abuse, or dementia