Main Outcome Measures: Cerebral SEP response (P300, Medoc Ltd., Israel) to thermal stimulation (550C). Warm-sensation threshold (WST), heat-pain threshold (HPT), Cold sensation threshold (CST) and cold pain threshold (CPT) by using Thermal sensory analyzer (TSA-2001,Medoc Ltd., Israel). Pain threshold to tactile stimulation will be measured by using Von-Frey hairs.