Synaptic Effect of Aδ-Fibers by Pulse-Train Electrical Stimulation

Shota Tanaka; Jose Gomez-Tames; Koji Inui; Shoogo Ueno; Akimasa Hirata; Toshiaki Wasaka

doi:10.3389/fnins.2021.643448

Synaptic Effect of Aδ-Fibers by Pulse-Train Electrical Stimulation

Front Neurosci. 2021 Apr 26:15:643448. doi: 10.3389/fnins.2021.643448. eCollection 2021.

Authors

Shota Tanaka¹, Jose Gomez-Tames^{1

2}, Koji Inui^{3

4}, Shoogo Ueno^{2

5}, Akimasa Hirata^{1

2

6}, Toshiaki Wasaka^{1

2}

Affiliations

¹ Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology, Nagoya, Japan.
² Center of Biomedical Physics and Information Technology, Nagoya Institute of Technology, Nagoya, Japan.
³ Department of Functioning and Disability, Aichi Developmental Disability Center, Institute for Developmental Research, Kasugai, Japan.
⁴ Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
⁵ Department of Biomedical Engineering, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
⁶ Frontier Research Institute for Information Science, Nagoya Institute of Technology, Nagoya, Japan.

Abstract

Electrical stimulation of specific small fibers (Aδ- and C-fibers) is used in basic studies on nociception and neuropathic pain and to diagnose neuropathies. For selective stimulation of small fibers, the optimal stimulation waveform parameters are an important aspect together with the study of electrode design. However, determining an optimal stimulation condition is challenging, as it requires the characterization of the response of the small fibers to electrical stimulation. The perception thresholds are generally characterized using single-pulse stimulation based on the strength-duration curve. However, this does not account for the temporal effects of the different waveforms used in practical applications. In this study, we designed an experiment to characterize the effects of multiple pulse stimulation and proposed a computational model that considers electrostimulation of fibers and synaptic effects in a multiscale model. The measurements of perception thresholds showed that the pulse dependency of the threshold was an exponential decay with a maximum reduction of 55%. In addition, the frequency dependence of the threshold showed a U-shaped response with a reduction of 25% at 30 Hz. Moreover, the computational model explained the synaptic effects, which were also confirmed by evoked potential recordings. This study further characterized the activation of small fibers and clarified the synaptic effects, demonstrating the importance of waveform selection.

Keywords: Aδ-fiber; electromagnetic model; intraepidermal electrical stimulation; multiscale model; nerve model; perception/pain; small fibers; synaptic model.