Only a few studies focus on clinical diseases like neuropathic pain or neurogenic pain. Little is known about the differences between normal and pathogenic pain processing. It is an opportunity to apply EEG, ERPs in the clinical fields. In many clinical conditions, brain lesions provide a chance to study the possible roles of one neural structure in pain integration and processing. In addition the applications of EEG/ERPs on clinical conditions may be help in the understanding about mechanism and genesis of pain in pathogenic conditions, the diagnosis of pathogenic pain, and the therapeutic aspects of these abnormal pain senses. One limit in the study of human pain is the inappropriate stimulation method. Evoked potentials by contact heat have previously been difficult to elicit due to slow temperature rise times associated with thermal stimulators. However recently, the CHEPS (Contact Heat-Evoked Potential Stimulator) is developed, which uses a newly developed heat-foil technology and can create a rapid heating rate (up to 70°C/sec). The baseline and peak temperature and the rising time can be precisely controlled. It provides a non-invasive technique in the investigation of human pain activation related to thermal and nociceptive pathways involved in pain processing. Unlike the heat stimulation delivered by laser, CHEPS can deliver noxious thermal stimuli repeatedly to a large area of skin to evoke a pain response of A-Delta and C fibers. In addition the rate of stimulation can be rapid to lead to the effect of temporal summation. When used with an EEG recording system, a patient's responses to pain perception and evoked potentials (EPs) can be recorded, which provide objective information about integrity of the nociceptive afferents of peripheral nerve system, spinal cord, as well as the brain response of different structures. The CHEPS provide the investigators a practical and convenient tool in clinical application to study pain. The investigators will use the CHEPS as stimulation for studying the heat evoked potentials and analyze the difference between the normal subjects and patients with peripheral nerve diseases. These might help to clarify the mechanism of neuropathic pain.