Noninvasive vagus nerve stimulation for neuromotor adaptations

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St. Pierre, Mitchell Adrien
Shinohara, Minoru
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Impaired motor function is often the result of neuromuscular disorders or advanced age. Neural adaptations associated with rehabilitative training are known to be correlated with the recovery and improvement of motor function. Enhancing corticospinal excitability via targeted plasticity during motor training can potentially facilitate neuromotor adaptations. The overarching goal of the current study was to explain the potential role of noninvasive vagus nerve stimulation in facilitating motor rehabilitation in a clinical setting. Twenty-four healthy young adults were pseudo-randomly divided into either the Sham group or tVNS group and completed five sessions of visuomotor training paired with outer ear stimulation. By pairing motor training on a novel visuomotor task with a noninvasive method of inducing cortical plasticity, we aimed to examine the effects on short-term and long-term motor adaptations. On average, measures of corticospinal excitability were greater in the tVNS group during the first session compared to the Sham group. Subjects in the tVNS group had a delayed profile of error reduction for the index finger compared to the Sham group, with the little finger showing a similar trend. Peak value of the cross-correlation function between finger forces also decreased across all subjects and is strongly correlated with the average decrease in root-mean-square error across subjects. This correlation suggests that the strategy of skill acquisition for the visuomotor task involves the consolidation of two synergistic finger forces into one functional output. The apparent delay in improvement for visuomotor skill in the tVNS group was counter to our initial expectations and emphasizes the need to further explore the underlying mechanisms of vagus nerve stimulation.
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