This study aims to investigate the effect of GEXP on brain regions involved in the processing of harmless tactile stimuli in CRPS-I and CLBP patients, as well as its effect on tactile discrimination thresholds. We hypothesize that GEXP will induce 1) an improvement of tactile discrimination thresholds, 2) a functional reorganization of primary and secondary somatosensory cortex (in regions related to the affected limb in CRPS-I; and to the back in LBP), 3) changes in activation of emotional brain circuits during non-noxious stimulation, 4) changes in resting state connectivity between emotional and sensory brain areas, 5) changes in measures reflecting white matter integrity. No systematic changes are expected in the healthy controls.