Thermal Detection Thresholds: Cool detection thresholds, which are mediated via A fibers and warm detection thresholds, which are mediated by small unmyelinated C fibers, will be determined using the TSA-II NeuroSensory Analyzer (Medoc Advanced Medical Systems U.S., Minneapolis, MN). The device consists of a computer controlled thermoelectric probe with a surface area of 9 cm2 that is attached using a velcro strap to the area of skin to be tested (thenar eminence and hypothenar eminence in the hands and the dorsal foot). For each trial the thermal stimulator starts at the thermo-neutral baseline temperature of 32oC, and increases for warming thresholds, or decreases for cooling thresholds, linearly at a rate of 1oC per second, until the subject pushes a button that stops and records the temperature and returns the unit to baseline temperature. Three trials are averaged for cool and for warm threshold for each site tested.