Thermal Pain: Thermal pain tolerance will be determined at the same sites and using the same method described above for thermal detection thresholds. The only difference is that for thermal pain trials, the subject will be instructed to push the control button (which immediately resets the stimulator back to baseline temperature) when the thermal stimulus (cold or hot) becomes painful. The TSA-II hardware automatically resets if the temperature reaches -10oC (for cooling) or 50oC (for heating) and the control button has not been pushed. This temperature range has been determined to not cause damage to skin or underlying tissue.