Background: Despite a broad clinical use, the mechanism of action of SCS is poorly understood. Current information suggests that the effects of SCS are mediated by a complex set of interactions at several levels of the nervous system including spinal and supraspinal mechanisms.
Aims: The study was undertaken to investigate the influence of SCS on distinct parameters of cortical excitability using single- and paired-pulse transcranial magnetic stimulation (TMS).
Methods: Five patients with chronic neuropathic pain were examined with the SCS stimulator on and off by means of TMS. Pain was assessed using a visual-analogue scale. Electrophysiological and pain parameters of patients during this procedure were compared by means of a linear mixed effect model.
Results: SCS induced a significant modulation of cortical excitability, especially by influencing the parameter "intracortical facilitation" (t=-2.657; df=8; p=0.029). A significant relationship between this parameter and "perceived pain" could be obtained (t=-4.798; df=8; p=0.002).
Conclusions: These results suggest that SCS is able to influence neurobiological processes at the supraspinal level and that clinical effects of SCS may be at least in part of cortical origin.