P 99. Effects of transcranial direct-current stimulation on diaphragm corticospinal pathway excitability

Abstract

Background Transcranial direct-current stimulation (tDCS) applied over the primary motor cortex induces polarity-dependent changes in excitability: anodal tDCS enhances cortical excitability as assessed using transcranial magnetic stimulation (TMS), whereas cathodal tDCS has the opposite effect. Objective In this randomized study, we assessed effects of anodal, cathodal, and sham tDCS on the diaphragmatic primary motor cortex. Methods Twelve healthy right-handed men received anodal, cathodal, and sham tDCS applied to the left diaphragmatic motor cortex. Motor-evoked-potential (MEP) recruitment curves were obtained by recording the surface electromyogram at the right 8th intercostal space during TMS at intensities ranging from the resting motor threshold (MT) to 130% of MT. For each condition, MEPs were recorded before (Pre) tDCS then after 10 min (Post1, at tDCS discontinuation in the anodal and cathodal sessions) and 20 (Post2) minutes. Results Both anodal and cathodal tDCS significantly decreased MEP amplitude at the right hemidiaphragm at both Post1 and Post2, versus Pre. MEP amplitude was unchanged versus Pre during the sham condition. Conclusion The effects of cathodal and anodal tDCS applied to the diaphragm motor cortex differ from those observed during tDCS of the limb motor cortex. This difference may be related either to the mechanisms involved in the effects of tDCS or to the diaphragm contractions during tDCS.