147. Dorsal transcutaneous spinal direct current stimulation (tsDCS) modulates human corticospinal system excitability

Abstract

Despite studies investigating how dorsal transcutaneous spinal direct current stimulation (tsDCS) influences the spinal ascending tract and reflexes, no data show whether and how it modulates function in the human corticospinal system. In 11 healthy subjects we recorded soleus H-reflex, F-waves and motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) from abductor hallucis (AH) and abductor digiti minimi (ADM) muscles before and at a different time-points (T0, T30) after anodal or cathodal tsDCS applied at 2.5 mA for 20 min over the thoracic spinal cord (T10–T12 level). Whereas cathodal tsDCS decreased MEP thresholds, after anodal tsDCS MEP thresholds from the lower limb muscles increased significantly ( F (2,20) = 5.01, p = 0.017). Similarly, after cathodal tsDCS, lower-limb MEP areas increased, whereas after anodal tsDCS they decreased significantly ( F (2,20) = 10.2, p = 0.0009). tsDCS left the lower-limb H/reflex and upperlimb F wave unchanged from baseline. Dorsal tsDCS modulates human corticospinal pathway function. The tsDCS-induced functional changes last for almost 20′ after DC offset and selectively affect muscle innervated by lumbosacral motorneurons caudal to the tsDCS stimulation site. These findings suggest that tsDCS acts on the corticospinal system leaving motoneuronal and neuromuscolar excitability unchanged.