DISSOCIATION OF CENTRALLY AND PERIPHERALLY INDUCED TRANSCRANIAL MAGNETIC STIMULATION EFFECTS IN NONHUMAN PRIMATES

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation method that is rapidly growing in popularity for studying causal brain-behavior relationships. However, its dose18 dependent centrally-induced neural mechanisms and peripherally-induced sensory co19 stimulation effects remain debated. Understanding how TMS stimulation parameters affect brain responses is vital for the rational design of TMS protocols. Studying these mechanisms in humans is challenging due to the limited spatiotemporal resolution of available non-invasive neuroimaging methods. Here, we leverage invasive recordings of local field potentials in a male and a female non-human primate (rhesus macaque) to study TMS mesoscale responses. We demonstrate that early TMS-evoked potentials show a sigmoidal dose-response with stimulation intensity. We further show that stimulation responses are spatially specific. We employ several control conditions to dissociate centrally-induced neural responses from auditory and somatosensory co-activation. These results provide crucial evidence regarding TMS neural effects at the brain circuit level. Our findings are highly relevant for interpreting human TMS studies and biomarker developments for TMS target engagement in clinical applications.