Non-invasive repetitive bi-hemispheric transcranial direct current stimulation (tDCS) may restore post-stroke bi-hemispheric balance by increase peri-lesional cortex activity and suppress abnormal inhibition from non-lesional hemisphere, and therefore enhance after-effects of rehabilitation. In this double-blind, randomized controlled trial, investigators aim to investigate whether multi-session, bihemispheric tDCS to the primary motor cortex (M1) in combination with upper extremity rehabilitation therapy affected motor functional outcome, ipsilesional motor circuit excitability using transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) measures.