Phase-Dependent Response to Afferent Stimulation During Fictive Locomotion: A Computational Modeling Study.

Soichiro Fujiki,Simon M Danner,Ilya A Rybak,Dai Yanagihara,Kazuo Tsuchiya,Shinya Aoi

doi:10.3389/fnins.2019.01288

Abstract

Central pattern generators (CPGs) in the spinal cord generate rhythmic neural activity and control locomotion in vertebrates. These CPGs operate under the control of sensory feedback that affects the generated locomotor pattern and adapt it to the animal's biomechanics and environment. Studies of the effects of afferent stimulation on fictive locomotion in immobilized cats have shown that brief stimulation of peripheral nerves can reset the ongoing locomotor rhythm. Depending on the phase of stimulation and the stimulated nerve, the applied stimulation can either shorten or prolong the current locomotor phase and the locomotor cycle. Here, we used a mathematical model of a half-center CPG to investigate the phase-dependent effects of brief stimulation applied to CPG on the CPG-generated locomotor oscillations. The CPG in the model consisted of two half-centers mutually inhibiting each other. The rhythmic activity in each half-center was based on a slowly inactivating, persistent sodium current. Brief stimulation was applied to CPG half-centers in different phases of the locomotor cycle to produce phase-dependent changes in CPG activity. The model reproduced several results from experiments on the effect of afferent stimulation of fictive locomotion in cats. The mechanisms of locomotor rhythm resetting under different conditions were analyzed using dynamic systems theory methods.

Highlights

The mammalian spinal cord contains neuronal circuitry that can generate a basic locomotor rhythm and produce the alternating flexor and extensor motoneuron activities underlying locomotion
The state of each neuron was characterized by the membrane potential Vi (i = F, E, IF, IE), where the indexes F and E are used for the rhythm generator (RG)-F and RG neuron (RG-E) neurons, respectively, and the indexes IF and IE are used for the Interneuron for RG-F (In-F) and Interneuron for RG-E (In-E) neurons, respectively
Stimulation was applied during the silent phase of RG-F (2.51 ≤ φs < 2π ), it caused the transition to the active phase to occur earlier and this advanced start decreased with φs

Summary

Introduction

The mammalian spinal cord contains neuronal circuitry that can generate a basic locomotor rhythm and produce the alternating flexor and extensor motoneuron activities underlying locomotion. This locomotor central pattern generator (CPG) can operate in the absence of sensory feedback (reviewed by Grillner, 1981; Rossignol, 1996; Orlovsky et al, 1999; Rossignol et al, 2006), afferent feedback plays a crucial role in adjusting the locomotor pattern to the motor task, the environment, and the biomechanical characteristics of the limbs and body (e.g., Pearson, 2004; Rossignol et al, 2006). Half-center type CPG models were previously used to reproduce some effects of sensory afferent stimulation on fictive locomotor pattern in cats (Rybak et al, 2006b)

Objectives

Methods

Results

Conclusion