Effect of transspinal direct current stimulation on afferent pain signalling in humans.

Anodal transspinal Direct Current Stimulation (tsDCS) has been suggested as a means to treat neuropathic pain by reducing pain signalling/processing and Laser Evoked Potentials (LEPs) likewise as a method to evaluate such reduction. However, results in previous studies are disagreeing. To evaluate these claims using rigorous methodology, LEPs were evoked from hands and feet in healthy volunteers. The N2 potential and three psychophysic parameters (general- and pinprick pain, warmth) were used to evaluate the signalling and appreciation of pain respectively. This was made at three time points; at baseline, directly- and 30 min after low thoracic tsDCS (20 min, 2.5 mA, cathode on shoulder). The study was randomized, cross over, double blinded and placebo controlled. At the group level, low thoracic anodal tsDCS produced reduced perceptions of all three tested pain qualities from the foot (p < 0.05 - p < 0.001). These reductions began during stimulation and became more pronounced during the 30 min after its cessation (p < 0.05 - p < 0.01). The LEP parameter alteration mirroring these changes was latency prolongation (p < 0.05 - p < 0.001) whereas amplitude reductions were in par with placebo stimulation. Similar but less pronounced and only transient (during stimulation, p < 0.05 - p < 0.001) changes, were seen for hand stimulation. The interindividual variation was large. The findings indicate that anodal tsDCS may become a technique to treat neuropathic pain by reducing pain signalling/processing and LEPs likewise a method to evaluate such reduction.