Design and validation of a closed-loop, motor-activated auricular vagus nerve stimulation (MAAVNS) system for neurorehabilitation

Abstract

Background: Studies have found that pairing vagus nerve stimulation (VNS) with motor activity accelerates cortical reorganization. This synchronous pairing may enhance motor recovery.

Objective: To develop and validate a motor-activated auricular vagus nerve stimulation (MAAVNS) system as a potential neurorehabilitation tool.

Methods: We created MAAVNS and validated its function as part of an ongoing clinical trial investigating whether taVNS-paired rehabilitation enhances oromotor learning. We compared 3 different MAAVNS EMG electrode configurations in 3 neonates. The active lead was placed over the buccinator muscle. Reference lead placements were orbital, temporal or frontal.

Results: The frontal reference lead produced the highest sensitivity (0.87 ± 0.07 (n = 8)) and specificity (0.64 ± 0.13 (n = 8)). Oral sucking reliably triggers MAAVNS stimulation with high confidence.

Conclusion: EMG electrodes placed on target orofacial muscles can effectively trigger taVNS stimuli in infants in a closed loop fashion.

Keywords: Closed-loop neuromodulation; MAAVNS; Motor rehabilitation; Oral feeding; Pediatrics; VNS; taVNS.

Conflict of interest statement

Declaration of competing interest DNC, MSG, DDJ, BWB are listed as inventors on pending patents assigned to the Medical University of South Carolina on the methods described in this manuscript.

Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.

Figures

Figure 1:

a) EMG lead placement for position C. Active lead on buccinator, reference lead on frontal eminence, ground lead in center of forehead. b) Overview of MAAVNS set up. EMG signals from facial muscles (1) were processed (2-5) and used to trigger stimulation (6, stim). c) Raw EMG signal was processed by amplifying, rectifying and integrating the signal. An activation threshold was set and calibrated to a visual suck, delivering a TTL output when a suck was detected.

Figure 2:

a) EMG lead placement for Configurations A, B, and C. b) Sensitivity and Specificity of EMG lead Configurations A, B, and C. This data demonstrates that both Configurations B and C had a sensitivity greater than 86%, however, Configuration C had a significantly greater specificity than Configuration B (64% compared to 40%).