Optimizing Current and Electrode Montage for Transcranial Direct Current Stimulation in Stroke Patients

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that can modulate cortical excitability of targeted brain regions. Various studies have investigated tDCS use in stroke patients with motor impairments (cumulatively about 200 cases). Although these studies are mostly "proof of concept" with small sample size, they do suggest that tDCS may improve motor function. However these two questions have not been addressed systematically:

• What is the optimal current for stroke patients?
• What is the optimal tDCS electrode montage for stimulation?

This proposal lays the scientific foundation for systematic application of tDCS in stroke recovery research by progressively increasing tDCS currents and montages that are both safe and efficacious in population with stroke.

Inclusion criteria

• 18-80 years old with a first-ever ischemic stroke that occurred at least 6 months ago;
• Finished rehabilitation therapy(including inpatient or outpatient Physical Therapy (PT) / Occupational Therapy (OT) / Speech Therapy (SP)) at least one month ago;
• Unilateral limb weakness with Fugl Meyer-Upper Extremity Scale score less than 56 (out of 66);
• Motor Evoked Potentials (MEP) is inducible on abductor pollicis brevis (APB) muscle on the affected side by TMS.

Exclusion criteria

• Primary intracerebral hematoma, or subarachnoid hemorrhage,
• Bihemispheric ischemic strokes;
• History of prior stroke or old infarct demonstrated on the CT or MRI or documented in medical records;
• Other concomitant neurological disorders affecting upper extremity motor function;
• Documented history of dementia before or after stroke;
• Documented history of uncontrolled depression or psychiatric disorder either before or after stroke which could affect their ability to participate in the experiment;
• Uncontrolled hypertension despite treatment, specifically Systolic blood pressure (SBP)/ Diastolic Blood Pressure (DBP) >= 180/100 mmHg at baseline;
• Presence of any MRI/tDCS/TMS risk factors: a) an electrically, magnetically or mechanically activated metal or nonmetal implant including cardiac pacemaker, intracerebral vascular clips or any other electrically sensitive support system; b) non-fixed metal in any part of the body, including a previous metallic injury to eye; c) pregnancy, since the effect of tDCS on the fetus is unknown; d) history of seizure disorder or post-stroke seizure; e) preexisting scalp lesion, bone defect or hemicraniectomy.