Single-pulse transcranial magnetic stimulation of the dorsolateral prefrontal cortex does not directly affect muscle sympathetic nerve activity in humans

Abstract

Transcranial magnetic stimulation (TMS) is applied both in research settings and clinically, notably in treating depression through the dorsolateral prefrontal cortex (dlPFC). We have recently shown that transcranial alternating current stimulation of the dlPFC partially entrains muscle sympathetic nerve activity (MSNA) to the stimulus. We, therefore, aimed to further explore the sympathetic properties of the dlPFC, hypothesizing that single-pulse TMS could generate de novo MSNA bursts. Microneurography was performed on the right common peroneal nerve in 12 participants. TMS pulses were then delivered to the ipsilateral dlPFC at resting motor threshold (MT) of the first dorsal interosseous muscle and at powers 20 below, 10 below, 10% above, and 20% above MT. The MT and 10% above MT intensities were also used to stimulate the right motor cortex and shoulder. Comparisons between stimulus intensities at the same site and between sites at the same intensities revealed no differences in MSNA burst frequency, burst incidence, or single MSNA spikes. Most stimulus trains, however, showed reduced burst frequency and incidence from baseline, regardless of site. This suggests that the TMS itself was evoking arousal-based sympathoinhibition, independent of dlPFC influences. It seems the dlPFC is capable of modulating MSNA but cannot directly generate bursts.