 Sympathetic Skin Response SSR. The disruption to the spinal autonomic pathways will be measured by electrophysiological recordings in the supine position, with the room temperature 21-25 deg C. Subjects will rest supine for at least 10 min before the beginning of the examination. Self-adhesive electrodes will be applied to the palmar and dorsal surfaces of the hands and plantar and dorsal surfaces of the feet. The median nerve will be stimulated 0.2 ms duration, 10-20mA intensity and 10 SSR samples will be recorded bilaterally from both hands and feet band pass of 3Hz to 3 kHz. The average latency ms and amplitude mV of the 10 SSRs will be calculated. 