This randomized, double-blinded, sham-controlled cross-over study will include three stimulation conditions: 1) anodal stimulation over the ipsilesional primary motor cortex, 2) cathodal one over the contralesional premotor cortex, 3) sham stimulation in chronic hemiparetic stroke patients.~Stroke participants (> 3 months after stroke) with moderate to severe motor impairments (Fugl-Meyer Motor Assessment - Upper Extremity score between 10-40, in absence of clinically defined sensory deficits) and an ischemic unilateral subcortical lesion will receive each type of stimulation for 20 minutes.~Their brain activity and behavior data will be collected for the outcome measures.~The patient time commitment in this study is approximately 7 weeks where subjects have 3 x 1-day intervention and measurements, with 2 weeks washout period in between.~The total number of potential enrolled subjects in this pilot study is 12.
Stroke is the leading cause of serious, long-term disability. The emergence of abnormal muscle synergies following a stroke presents a major limitation to the recovery of independent function. Despite the development of many interventions for movement recovery post-stroke, rehabilitation treatments are minimally effective to the muscle synergy impairment. Previous studies have found that muscle synergy impairment is associated with the damage to the corticospinal tract and the maladaptive recruitment of the contralesional cortico-reticulospinal tract. The investigators hypothesize that facilitating the damaged cortico-spinal tract (via primary motor cortex) and/or inhibiting the contralesional cortico-reticulospinal tract (via dorsal premotor cortex) will reduce muscle synergy impairment. In this pilot project, the investigators propose to run a proof-of-concept pilot trial to evaluate the effect of the targeted high-definition transcranial direct current stimulation (HD-tDCS) on mitigating muscle synergy impairment.