 The purpose of this study is to evaluate the effects of the SCS on sensory perceptions of patients with chronic pain CRPS, FBSS. Sensorial perception tests will be carried out in accordance with a standardized procedure Rolke et al. Pain, 2006. For non-implanted patients, an initial visit will be conducted before the operation. For all participants, two other visits will take place at least 6 months after the operation to perform the tests with and without stimulation. 