Comparison of existing electrode designs for preferential activation of cutaneous nociceptors

Abstract

Objective. Over the recent years, several small area electrodes have been introduced as tools for preferential stimulation of small cutaneous nerve fibers. However, the performance of the electrodes is highly debated and have not previously been systematically compared. The electrodes have been developed empirically and little is known about the electrical potential they produce in the skin, and how this influences the nerve fiber activation. The objective of the present study was to develop and validate a computational model to compare the preferential stimulation of small fibers for electrodes of different designs.Approach. A finite element model of the skin was developed and coupled with an Aβ-fiber and an Aδ-fiber multi-compartmental nerve fiber model, to describe the current spread and consequent nerve fiber activation produced by five different surface electrodes; intraepidermal, planar concentric, pin, planar array, and patch. The model was validated through experimental assessments of the strength-duration relationship, impedance and reaction times.Main results. The computational model predicted the intra-epidermal electrode to be the most preferential for small fiber activation. The intra-epidermal electrode was however also found to be the most sensitive to positioning relative to nerve fiber location, which may limit the practical use of the electrode.Significance. The present study highlights the influence of different electrode design features on the current spread and resulting activation of cutaneous nerve fibers. Additionally, the computational model may be used for the optimization of electrode design towards even better preferential stimulation of small fibers.

Electrical Characterisation of Aδ-Fibres Based on Human in vivo Electrostimulation Threshold

“…The difference in the myelin thickness influenced the amount of charge stored in the fibre, so the variation in the short pulse width was large. The chronaxie was estimated in a recent study (Poulsen et al, 2020) as 599-756 µs, which is twice larger than that in our study. However, only four different durations (0.1, 0.5, 1, and 10 ms) were considered in that study.…”

“…Only two studies have measured perception threshold to derive S-D curves but were not specific to one type of small fibre (co-activation of different small fibres) (Hennings et al, 2017). Recently, Poulsen et al (2020) investigated S-D curves of Aδfibres for different electrodes; the rheobase was estimated in terms of injection current, which is not induced by physical quantity. Moreover, only a few pulse durations were considered.…”

Observation of Nociceptive Processing: Effect of Intra-Epidermal Electric Stimulus Properties on Detection Probability and Evoked Potentials

“…A well-defined nociceptive sensory input can be generated by preferential stimulation of nociceptive Aδ afferents in the skin using intra-epidermal electric stimulation (Inui et al 2002). This technique has been shown to preferentially activate nociceptive afferents when applied at less than two times the detection threshold (Mouraux et al 2010;Poulsen et al 2020). Recently, we developed a method to concentrate stimulation around this (drifting) detection threshold, and measure stimulus-response pairs and evoked potentials in response to these nociceptive stimuli (van den Berg et al 2020).…”

Use-Dependent Plasticity Enhances Nociceptive and Non-Nociceptive Somatosensory Cortical Responses in Healthy Individuals

“…Detection thresholds and reaction times confirmed that nociceptive and non-nociceptive stimulation selectively activated their corresponding fibers. That is, according to the kind of fibers and the physical characteristics of each electrode (Poulsen et al, 2020), nociceptive stimulation required lower stimulus intensity and generated slower reaction-times, in line with the characteristics of Aδ-fibers, whereas non-nociceptive stimulation required higher stimulus intensity and generated faster reaction-times, in line with the characteristics of Aβ-fibers.…”