RecruitingPhase 2Clinical trialFrom Nerve to Brain: Toward a Mechanistic Understanding of Spinal Cord Stimulation in Human SubjectsThis is a multicenter prospective study of patients who currently have stably implanted spinal cord simulators. Patients will be randomly assigned to turn on or off their spinal cord stimulators for two week intervals up to six weeks after enrollment, and on the final day of study participation, for one hour intervals, in a multi-crossover design. In a subset of patients we will also perform combined positron emission tomography/magnetic resonance imaging at baseline, week 2 and week 4.