 TMS was used to assess the effects of BoNT on SICI in subjects with arm dystonia. SICI in distal hand muscle increases at one month after BoNT injections and returns to the previously abnormal levels of excitability at three months. It can be speculated that the BoNT therapy to arm muscles modulates the afferent input from muscles, which probably results in reorganization of the motor cortex. It is not clear if the physiological change induced by BoNT therapy had any correlation with the clinical improvement. In addition, it is not clear if the change in motor cortex excitability ultimately affects the corticospinal drive to the dystonic muscles. 