The purpose of this study is to determine whether patients with neuropathic pain has abnormal excitability in somatosensory cortex and abnormal sensory-motor connections.

There are several brain areas responsible for neuropathic pain reported in functional image studies, including primary sensory cortex, insula, and anterior cingulate gyrus. However, it is few informations about the functional status of these areas. Besides, the reason of the individual variability about the developement of neuropathic pain remains unknown. It is lack of satisfactory explanation about why some people developed neuropathic pain in certain diseased situation (for example, type 2 diabetes), while others do not.

We hypothesis that patients with neuropathic pain has abnormal cortical excitability and plasticity in certain brain area. Therefore developed neuropathic pain certain diseased condition while others not. Therefore, we will use multimodal electrophysiology tools,such as transcranial magnetic stimulation, peripheral nerve stimulation, and contact heat evoke potential to monitor the cortical excitability and plasticity non-invasively.

Inclusion Criteria:

• Healthy volunteers
• patients with pain resulted from dysfunction of peripheral or central nervous system
• the disorders of peripheral nerves are diagnosed by nerve conduction study, quantitative sensory test, quantification of skin innervation or contact heat evoked potentials
• lesion of central nervous system should be confirmed by neuroimage.

Exclusion Criteria:

• previous history of epilepsy, seizure disorders or major head injury
• previous brain surgery or intracranial metalic implant
• implanted devices as cardiac pacemaker
• pregnant subjects
• patient with severe cardiac or pulmonary disease who potentially cannot tolerate stress

Primary care clinic healthy volunteer