Intra-operative neuromonitoring (XLTEK/NATUS EP Protektor)
DeviceDevice: Intra-operative neuromonitoring A XLTEK/NATUS EP Protektor machine (at MGH) or a Cadwell Cascade Elite neuromonitoring machine (at BWH), both FDA approved for intra-operative neuromonitoring, will deliver the electrical stimulus applied transcranially to stimulate the motor cortex, while motor evoked responses will be recorded from different myotomes from both upper limbs. Also the same equipment will deliver electrical stimulus to stimulate peripherally the median and ulnar nerves at the wrists, with recording of the thalamocortical potentials in the scalp channels.