The main non-invasive neuromodulatory techniques: an infographic

Abstract

INTRODUCTION: This infographic aims to present the main non-invasive neuromodulatory techniques that can be used to assess and/or modulate central nervous system excitability. Single- and paired-pulse transcranial magnetic stimulation (TMS) can be used to assess brain excitability through the delivery of magnetic pulses over the cerebral cortex. The motor evoked potential is an indirect measure of motor cortex excitability and is the most used cortical measure of excitability. RESULTS: Neuromodulation may be achieved through several techniques, which may be used to promote top-down or bottom-up effects. Among the top-down techniques is direct current stimulation (DCS) which can change its nomenclature according to the stimulation target, for example, transcranial (tDCS), or cerebellar (ctDCS). In addition, also can be included in top-down techniques  the  transcranial random noise stimulation (tRNS), transcranial alternate current stimulation (tACS), and repetitive TMS (rTMS). On other hand, the bottom-up techniques include the peripheral electrical stimulation (PES), transcutaneous auricular vagus nerve stimulation (taVNS), transcutaneous spinal direct current stimulation (tsDCS), and repetitive peripheral magnetic stimulation (rPMS). CONCLUSION: The neuromodulatory effects are dependent on several parameters that can be specific to physical principles (electrical or magnetic). For example, in repetitive P/TMS the frequency, type and angular orientation of coil, distance between the coil and the brain, pulse waveform, and pattern of stimulation are presented as important parameters able to interfere with the quality of stimulation. The same can be observed in tDCS, ctDCS, and tsDCS with the polarity and shape and montage of electrode, intensity, site and duration of stimulation, and current density.