Mapping (10 minutes): A 5-by-5 cortical grid of target (25 targets in total) with the interval 1 cm (4X4 cm2) will be generated over the motor cortex area in the Neuronavigation System. A response map based on the peak-to-peak amplitude of MEP will be created in real time by a customized program (LabVIEW, v2012, National Instruments, Austin, TX) program.