 In this study, the investigators will focus on the physiological effects of BoNT using broader TMS measures of motor cortex excitability. The central hypothesis is that BoNT modulates the motor cortex excitability and the corticospinal drive to the muscles and that these physiological effects of BoNT will have a clear correlation with the clinical response. To test this hypothesis, the investigators plan to measure the corticospinal drive to dystonic muscles using electromyographic EMG spectral analysis. They will record the clinical outcome with the Toronto Western Spasmodic Torticollis Rating Scale TWSTRS which is a standardized validated rating scale for PCD. 