Effect of spinal transcutaneous Direct Current Stimulation on somatosensory evoked potentials in humans

Objective: Invasive stimulation of the spinal cord is used to treat a number of pathological conditions. Aiming to modulate human spinal cord function non-invasively, we evaluated whether transcutaneous direct current (DC) stimulation induces long-lasting changes in conduction along the sensory spinal pathways. Methods: Somatosensory evoked potentials (SEPs) by posterior tibial nerve and by median nerve stimulation were recorded, before, at current offset and at 20 min after transcutaneous anodal or cathodal DC stimulation over the thoracic spinal cord (2.5 mA, 15 min) in a group of 12 healthy subjects. Results: Whereas both polarities left the spinal (N22) and the cortical potentials (P39) unchanged, anodal transcutaneous spinal DC stimulation decreased significantly by about 25% the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30) for at least 20 min. Thoracic transcutaneous spinal cord stimulation left median nerve SEPs unchanged. Conclusions: Transcutaneous DC stimulation over the thoracic spinal cord induces changes in conduction along human lemniscal pathway that persist after stimulation ends. Significance: Our results support the use of transcutaneous DC stimulation as a novel tool for non-invasive spinal neuromodulation. Because the method is non-expensive and simple, it can be tested in patients with disorders presently treated with invasive procedures.