Trial Outcomes & Findings for Noninvasive Vagus Nerve Stimulation (VNS) for Neuromotor Adaptations (NCT NCT03628976)

Participants were recruited from May 2019 to June 2021 through flyers posted in the classroom buildings and recreational buildings on the Georgia Tech campus.

There was no significant event in the study that occurred after participant enrollment.

Noninvasive Vagus Nerve Stimulation (VNS) for Neuromotor Adaptations

Visuomotor skill was assessed with the amount of force error against the target trajectory. In the visuomotor task, subjects produced finger force against a force transducer to match a target trajectory as close as possible. The target was made of three low-frequency sinusoids with each sinusoid at different frequencies and amplitudes. This pattern spanned 20 s. The data in the middle 16 s were used for data analysis. For determining the visuomotor skill, the deviation of produced force from the target trajectory was calculated as the root-mean-square error. In this calculation, the difference between the target and produced force at each sampling point was squared, the squared values were summed across sampling points, and the squared root value of the summed value was determined and normalized to the maximal voluntary contraction (MVC) force. The data were expressed as the ratio of the baseline value (no unit). A lower value is considered a better outcome.

Brain excitability was assessed with motor evoked potential (MEP) amplitude of the resting first dorsal interosseus muscles as resting corticospinal excitability. Surface EMG electrodes were attached over the muscle in a belly-tendon configuration. Subjects received single-pulse TMS to evoke MEP in the muscle. MEP was obtained from the surface EMG using a high-gain EMG preamplifier. Peak-to-peak- amplitude of MEP in response to TMS were averaged across the intensities of 115-160% relative to the resting motor threshold. Additionally, maximal M-wave amplitude was obtained by stimulating the ulnar nerve that innervates the muscle. MEP amplitude was normalized to the maximal M-wave amplitude of the muscle, so it was expressed in % of maximal M-wave. A higher value is considered higher brain excitability and a better outcome.

Central noradrenaline was assessed indirectly with salivary amylase activity. Saliva was sampled via salivette strips in the resting state before and after the training. Subjects were seated and rested for 5 minutes before sampling the samples. Collected saliva samples were immediately analyzed by using a dry-chemistry system automatically. Three saliva samples were analyzed and averaged across samples. Salivary amylase activity was measured and expressed in kU/I (kilo units per liter).