 In contrast to previous thoughts reflected in the name RSD, it appears that there is reduced sympathetic nervous system outflow, at least in the affected region (although there may be sympatho-afferent coupling).Wind-up (the increased sensation of pain with time) and central nervous system (CNS) sensitization are key neurologic processes that appear to be involved in the induction and maintenance of CRPS.Compelling evidence shows that the N-methyl-D-aspartate (NMDA) receptor has significant involvement in the CNS sensitization process.