The central objective of this application is to explore the neural substrate of personalized tDCS (ptDCS) and to determine whether the paradigm for each stroke patient can predict the amount of sustained clinical improvement through increased connectivity as measured by a biomarker of plasticity.

This is a randomized, sham controlled double masked parallel group study with optional crossover of chronic (>3mo from stroke onset) ischemic or hemorrhagic stroke patients to test the effect of ptDCS on a cerebral connectivity biomarker of plasticity during stimulation and after 10 treatment of up to 2 mA ptDCS. PtDCS will be performed during the first 20 minutes of occupational therapy targeting the weaker arm compared to sham. Patients will have the option to cross over after the completion of 1-month follow-up and will complete the same procedures with real tDCS if they were in the sham group.

Inclusion Criteria:

• Symptomatic ischemic or hemorrhagic stroke verified by computerized axial tomography or magnetic resonance imaging resulting in hemiparesis (MRC 1-4).
• Age more than 18, Male or Female, All racial and ethnic groups
• Entry into the study >3 months post onset
• Modified Ashworth Scale Score <3 in the involved upper extremity
• Passive range of motion within functional ranges at the shoulder, elbow, wrist and hand
• Able to follow 2 step commands

Exclusion Criteria:

• Patients with history of severe alcohol or drug abuse, psychiatric illnesses like severe depression, poor motivational capacity, or severe language disturbances, particularly of receptive nature or with serious cognitive deficits (defined as unable to follow study instructions).
• Patients with bilateral paresis, or weakness or sensory damage due to peripheral causes (e.g. peripheral nerve injury, muscle or orthopedic injury etc.)
• Patients with severe uncontrolled medical problems (e.g. cardiovascular disease, severe rheumatoid arthritis, active joint deformity of arthritic origin, active cancer or renal disease, any kind of end-stage pulmonary or cardiovascular disease, or a deteriorated condition due to age,epilepsy or others).
• Patients with unstable cardiac arrhythmia.
• Pregnancy
• Patients with metallic implants in the head, patients with pacemakers, patients with craniotomies, including burr holes who cannot be safely stimulated
• Patients with seizures
• Non-English speaking individuals will only be eligible if they can provide the appropriate translator for all the sessions of the study as no funding is available to pay for such services.