Analysing vagus nerve spontaneous activity using finite element modelling

Abstract

Objective. Finite element modelling has been widely used to understand the effect of stimulation on the nerve fibres. Yet the literature on analysis of spontaneous nerve activity is much scarcer. In this study, we introduce a method based on a finite element model, to analyse spontaneous nerve activity with a typical bipolar electrode recording setup, enabling the identification of spontaneously active fibres. We applied our method to the vagus nerve, which plays a key role in refractory epilepsy. Approach. We developed a 3D model including dynamic action potential propagation, based on the vagus nerve geometry. The impact of key recording parametersinter-electrode distance and temperatureand uncontrolled parametersfibre size and position in the nerveon the ability to discriminate active fibres were quantified. A specific algorithm was implemented to detect and classify action potentials from recordings, and tested on six rat in-vivo vagus nerve recordings. Main results. Fibre diameters can be discriminated if they are below 3 µm and 7 µm, respectively for inter-electrode distances of 2 mm and 4 mm. The impact of the position of the fibre inside the nerve on fibre diameter discrimination is limited. The range of active fibres identified by modelling in the vagus nerve of rats is in agreement with ranges found at histology. Significance. The nerve fibre diameter, directly proportional to the action potential propagation velocity, is related to a specific physiological function. Estimating the source fibre diameter is thus essential to interpret neural recordings. Among many possible applications, the present method was developed in the context of a project to improve vagus nerve stimulation therapy for epilepsy.

Vagus Nerve Electroneurogram-Based Detection of Acute Pentylenetetrazol Induced Seizures in Rats

“…For those reasons we expect to observe higher VENG signal amplitudes, 46 and therefore the removal of the epineurium might not be necessary. On the other hand, as spike amplitude drastically decrease with the distance to the surface, 46 signals of fibers deeper in the nerve will drown in the high amplitude signals of superficial fibers. This will result in a limited recording depth and the miss of signals deep in the nerve.…”

A method to establish functional vagus nerve topography from electro-neurographic spontaneous activity

“…A fiber segment with a length of 2 cm ( Figure S3 B) was modeled for each different value of the fiber diameter, which was sampled from a normal distribution truncated at [10,13] μm for Aα fibers and from a normal distribution for an Aβ fiber truncated at [6,12] μm for Aβ fibers. As in Smets et al., 34 we modeled only myelinated fibers, and unmyelinated fibers (C fibers) were not considered. This is because the amplitude of an action potential (AP) is proportional to the square of the fiber diameter, 35 and because the diameter of the myelinated fibers is larger than that of the unmyelinated fibers, the amplitude of the APs of the myelinated fibers turns out to be larger, causing the unmyelinated fibers to have a less predominant contribution in an in vivo recording.…”

Chronic recording of the vagus nerve to analyze modulations by the light–dark cycle

“…Both VENG and EEG channels had an isolated ground placed on the forehead of the rat (respectively, VENG GND and EEG GND, see figure 1(a)). We used the VENG bipolar configuration as the input signal to ensure a large interelectrode distance [17,18]. We used P1-F1 derivation as the EEG input signal.…”