Modulating parameters of excitability during and after transcranial direct current stimulation of the human motor cortex

Introduction: Weak direct current stimulation (tDCS) of the human motor cortex results in excitability shifts which occur during and after stimulation. These are polarity-specific with anodal tDCS enhancing excitability, and cathodal reducing it. To explore the origin of this excitability modulation, we measured the input/output curve and motor thresholds as global parameters of cortico-spinal excitability, and determined intracortical inhibition and facilitation, as well as facilitatory indirect wave (I-wave) interaction. Measurements were performed during short-term tDCS, which elicits no after-effects, and fo…