Effects of transcutaneous spinal DC stimulation on plasticity of the spinal circuits and corticospinal tracts in humans

The aim of this exploratory study was to investigate the effects of transcutaneous spinal direct current stimulation (tsDCS) on the plasticity of spinal circuits and corticospinal tracts in humans. Ten healthy volunteers participated in this single-blind, sham-controlled cross-over study. Reciprocal inhibition and D1 inhibition of the soleus H-reflex (experiment 1), and motor evoked potentials (MEPs) of the tibialis anterior and soleus muscles induced by transcranial magnetic stimulation over the motor cortex (experiment 2) were recorded before and after anodal tsDCS (2 mA, 15 min) or sham (2 mA, 15 sec) delivered at the thoracic spine level. In experiment 1, anodal tsDCS significantly decreased the amount of D1 inhibition at least 15 min after the end of stimulation, but did not affect the amount of reciprocal inhibition. In experiment 2, anodal tsDCS did not affect the amplitude of MEPs. The present results provide further evidence that tsDCS can induce short-term plasticity in human spinal reflex circuits.