Behavioral and electrophysiological evidence for GABAergic modulation through transcutaneous vagus nerve stimulation

Objective: Transcutaneous vagus nerve stimulation (tVNS) has been hypothesized to modulate gamma-aminobutyric (GABA) transmission in the human brain. GABA in the motor cortex is highly correlated to measures of automatic motor inhibition that can be obtained in simple response priming paradigms. To test the effects of tVNS on GABA transmission, we measured tVNS-induced alterations in behavioral and electrophysiology during automatic motor inhibition. Methods: Participants were 16 young, healthy adults (8 female). We combined a subliminal response priming paradigm with tVNS and EEG measurement. In this paradigm, automatic motor inhibition leads to a reversal of the priming effect, a phenomenon referred to as the negative compatibility effect (NCE). We compute the NCE separated by response hands, hypothesizing a modulation of the left-hand NCE. Using EEG we measured readiness potentials, an established electrophysiological index of cortical motor preparation. Results: As hypothesized, for the ipsilateral hand/contralateral hemisphere, compared to sham stimulation, tVNS increased the NCE and modulated the electrophysiological readiness potentials. Conclusion: Our results indicate that tVNS is selectively affecting the GABAergic system in the motor system contralateral to the stimulated ear as reflected in a behavioral and electrophysiological modulation. Significance: We provide first combined behavioral and electrophysiological evidence for direct GABAergic neuromodulation through tVNS. (C) 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.