Local field potentials of the auricular Vagus nerve - In-silico stimulation and recording

Abstract

Measuring the activity of the parasympathetic and sympathetic nervous system (PSNS and SYNS, respectively) has always been a challenge. Until recently, usually non-invasive but unspecific heart rate variability was used, which mainly reflects activity of the cardiovagal PSNS branch only. Alternatively, invasive but specific microneurography has shown great resolution in measuring local SYNS activity in mammals. We propose the auricle, specifically the vagally innervated regions of the Cymba Concha and the cavity of Concha, as a potential region for measuring local field potentials (LFP) which we hypothesize to reflect both the afferent PSNS and efferent SYNS autonomous activity. Using the NEURON Simulation Environment, a simple computational model of a single auricular vagus nerve branch under human skin was developed, stimulated intracellularly and differential LFPs were monitored using two recording electrodes. To gain a better understanding of the behavior, e.g. timing and shape of individual LFPs and electrode position with respect to fiber position was varied. Furthermore, different fiber diameters ranging from 5.7μ m to 16μ m were implemented into the model. The differential LFPs usually show a hexaphasic form with a maximum differential amplitude of 3.05nV. Two individual peaks were always clearly visible, with a peak-topeak time depending not only on inter-electrode-distance but also on fiber diameter. Single LFPs showed a change in shape from biphasic to triphasic depending on electrode-to-fiber distance and fiber diameters. Our computational results will help in interpreting our experimental data and distinguishing actual PSNS activity-related vagal peaks from SYNS activityrelated interference generated by smooth muscles. In addition, the presented model will support building more complex models resembling auricular vagus nerve fibers in bundles and realistic geometric layout.