Determine the Effect of Targeted High-definition Transcranial Direct Current Stimulation (tDCS) on Reducing Post-stroke Upper Limb Motor Impairments

This sham-controlled cross-over study design will include four visits: 1) anodal stimulation targeting the ipsilesional hemisphere, 2) cathodal one at the contralesional hemisphere, 3) bilateral stimulation with anodal on the ipsilesional hemisphere and cathodal on the contralesional hemisphere and 4) a sham stimulation visit. The sequence of the stimulations will be randomized and double-blinded (assessor and participants). After each intervention, there will be at least 2 weeks wash-out period before participants receive the next intervention and assessments. Each visit will last up to 3 hours including the preparation time and breaks. We will use neuro-navigation high-definition tDCS (NNG HD-tDCS) to target specific brain regions in a more precise way than before. A subject-specific head model will be built to evaluate the effect of lesion size and location on the electrical field of tDCS. The MR images (if available, otherwise CT images) will be used to build this subject-specific head model. The stimulation electrode montage and inter-electrode distance will be carefully examined by computer simulation to determine the optimal setup and dosage for NNG HD-tDCS. The patient time commitment in this study is approximately 10 weeks where subjects have 4 x 1-day intervention and measurements, with 2 weeks washout the period in between. The total number of potential enrolled subjects in this pilot study is 30.