Effects of transcranial direct current stimulation of the primary sensory cortex on somatosensory perception

BackgroundTranscranial direct current stimulation (tDCS) is able to modify cortical excitability and activity in humans.ObjectiveThe aim of the present study was to analyze the effects of tDCS of the primary sensory cortex (SI) on thermal and mechanical perception, assessed by quantitative sensory testing (QST).MethodsThe comprehensive QST protocol encompassing thermal and mechanical detection and pain thresholds as devised by the German Research Network on Neuropathic Pain (DFNS) was applied to skin areas innervated by the radial and median nerve of 12 healthy subjects, who were examined before and after each tDCS stimulation type. Anodal, cathodal, and sham tDCS was applied at a 1 mA current intensity with the active electrode placed over the left primary sensory cortex (SI) and the reference electrode above the right orbit for 15 minutes.ResultsAfter cathodal tDCS cold detection threshold (CDT) significantly increased in the contralateral (P < .01) and ipsilateral hand (P < .05) as compared to baseline condition and sham stimulation, after cathodal stimulation significantly increased warm detection threshold (WDT) was observed in the contralateral hand when compared with the baseline condition (P < .05) but not with sham stimulation. Thermal pain as well as mechanical detection and pain thresholds remained unaltered.ConclusionsCathodal tDCS of the primary sensory cortex significantly reduced the sensitivity to Aδ-fiber-mediated cold sensation, C-fiber-mediated warm sensation was reduced only compared with baseline, whereas Aß-fiber-mediated somatosensory inputs were less affected. Our results correspond with our previous observations of primary motor cortex tDCS effects on QST parameters.