Transcranial direct current stimulation modulates motor responses evoked by repetitive transcranial magnetic stimulation

Introduction Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are non-invasive techniques able to induce changes in corticospinal excitability. In this study, we combined rTMS and tDCS to understand possible interactions between the two techniques, and investigate whether they are polarity dependent. Materials and methods Eleven healthy subjects participated in the study. Each patient underwent both anodal and cathodal conditioning tDCS in two separate sessions; brief 5 Hz-rTMS trains were delivered over the primary motor cortex at an intensity of 120% the resting motor threshold (RMT) before tDCS (T0), immediately after (T1) and 10 min after current offset (T2). We then analysed changes induced by cathodal and anodal tDCS on TMS variables. Results Our results showed that in both anodal and cathodal sessions, the motor evoked potential (MEP) amplitude increased significantly in size before stimulation (T0). Conversely, after anodal tDCS, the MEP facilitation measured at T1 and T2 was absent, whereas after cathodal tDCS it was preserved. Conclusions Our findings provide new direct neurophysiological evidence that tDCS influences primary motor cortex excitability.