Effects of auricular vagus nerve stimulation and electrical earlobe stimulation on motor‐evoked potential changes induced by paired associative stimulation

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Abstract
Paired associative stimulation (PAS) is a combination of transcranial magnetic stimulation (TMS) and peripheral nerve stimulation (PNS). PAS can induce long‐term potentiation (LTP)‐like plasticity in humans, manifested as motor‐evoked potential (MEP) enhancement. We have developed a variant of PAS (“high‐PAS”), which consists of high‐frequency PNS and high‐intensity TMS and targets spinal plasticity and promotes rehabilitation after spinal cord injury (SCI). Vagus nerve stimulation (VNS) promotes LTP‐like plasticity and enhances recovery in SCI and stroke in humans and animals when combined with repetitive motor training. We combined high‐PAS with simultaneous noninvasive transcutaneous auricular VNS (aVNS) to determine if aVNS enhances the extent of PAS‐induced MEP amplitude increase. Sixteen healthy participants were stimulated for 20 min in four different sessions (PAS, PAS + aVNS, PAS + shamVNS, and aVNS) in a randomized single‐blind setup. MEPs were measured before, immediately after, and at 30, 60, and 90 min post‐stimulation. Stimulation protocols with PAS significantly potentiated MEPs (p = 0.005) when compared with aVNS (p = 0.642). Although not significant, MEP enhancement observed after PAS (43.5%) is further increased by aVNS (49.7%) and electrical earlobe stimulation (63.9%). Our aVNS setup failed to significantly enhance the effect of PAS, but sham VNS revealed a trend towards enhanced plasticity. Optimization of auricular VNS stimulation setup is required for possible tests of patients with SCI.
Funding Information
  • Wings for Life
  • Research Council of Finland

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