Modulatory effects of anodal transcranial direct current stimulation on perception and pain thresholds in healthy volunteers

Background and purpose: We aimed to evaluate whether transcranial direct current stimulation (tDCS) is effective in modulating sensory and pain perception thresholds in healthy subjects as to further explore mechanisms of tDCS in pain relief. Methods: Twenty healthy subjects received stimulation with tDCS under four different conditions of stimulation: anodal tDCS of the primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), occipital cortex (V1), and sham tDCS. The order of conditions was randomized and counterbalanced across subjects. Perception threshold and pain threshold to peripheral electrical stimulation of the right index finger were evaluated by a blinded rater. Results: The results showed a significant effect of the interaction time versus stimulation condition for perception (P = 0.046) and pain threshold (P = 0.015). Post hoc comparisons revealed that anodal stimulation of M1 increased both perception (P < 0.001, threshold increase of 6.5%) and pain (P = 0.001, threshold increase of 8.3%) thresholds significantly, whilst stimulation of the DLPFC increased pain threshold only (P = 0.046, threshold increase of 10.0%). There were no significant effects for occipital or sham stimulation. Conclusions: These results show that both M1 and DLFPC anodal tDCS can be used to modulate pain thresholds in healthy subjects; thus, the mechanism of tDCS in modulating pain involves pathways that are independent of abnormal pain-related neural activity.