Transcutaneous spinal direct current stimulation inhibits nociceptive spinal pathway conduction and increases pain tolerance in humans

Despite concerted efforts from pharmacologic research into neuropathic pain, many patients fail to achieve sufficient pain relief with medication alone. For this reason, increasing interest centres on neurostimulation techniques. We assessed whether transcutaneous spinal direct current stimulation (tsDCS) modulates conduction in ascending nociceptive spinal pathways. We measured changes induced by anodal and cathodal tsDCS over the thoracic spinal cord on face- and foot-laser evoked potentials (LEPs) and foot-cold pressor test responses in 20 healthy subjects. Whereas anodal tsDCS reduced the amplitude of the N1 and N2 components of foot-LEPs (P<0.05) neither anodal nor cathodal tsDCS changed LEPs evoked by face stimulation. Pain tolerance to the cold pressor test was significantly higher after anodal than after cathodal tsDCS (P<0.05). Conversely, no difference was found in the pain threshold or pain ratings to the cold pressor test between the two polarity conditions. Our data suggest that anodal tsDCS over the thoracic spinal cord might impair conduction in the ascending nociceptive spinal pathways, thus modulating LEPs and increasing pain tolerance in healthy subjects.