6. The investigator will then perform a single scalp biopsy procedure at the site of central sensitization testing, according to standard of care practices. The 2mm specimen will be placed into formalin for routine paraffin-embedding. The 3mm specimen will be placed into a special fixative that optimizes immunohistochemistry on frozen sections to detect antigens expressed by nerves. These specimens will be labeled with the subjects/control's unique identifying code only and without personal health information.