Adaptive hindlimb split-belt treadmill walking in rats by controlling basic muscle activation patterns via phase resetting

Soichiro Fujiki,Dai Yanagihara,Tetsuro Funato,Yota Sato,Kazuo Tsuchiya,Shinya Aoi

doi:10.1038/s41598-018-35714-8

Soichiro Fujiki, Dai Yanagihara + Show 4 more

Open Access

https://doi.org/10.1038/s41598-018-35714-8

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Abstract

To investigate the adaptive locomotion mechanism in animals, a split-belt treadmill has been used, which has two parallel belts to produce left–right symmetric and asymmetric environments for walking. Spinal cats walking on the treadmill have suggested the contribution of the spinal cord and associated peripheral nervous system to the adaptive locomotion. Physiological studies have shown that phase resetting of locomotor commands involving a phase shift occurs depending on the types of sensory nerves and stimulation timing, and that muscle activation patterns during walking are represented by a linear combination of a few numbers of basic temporal patterns despite the complexity of the activation patterns. Our working hypothesis was that resetting the onset timings of basic temporal patterns based on the sensory information from the leg, especially extension of hip flexors, contributes to adaptive locomotion on the split-belt treadmill. Our hypothesis was examined by conducting forward dynamic simulations using a neuromusculoskeletal model of a rat walking on a split-belt treadmill with its hindlimbs and by comparing the simulated motions with the measured motions of rats.

Highlights

Locomotor adaptability in animals has been investigated using a split-belt treadmill, which has two parallel belts whose speeds are controlled independently to prepare left–right symmetric and asymmetric environments for walking[1,2,3,4,5,6,7,8,9,10]
Ivanenko et al.[14,15] showed that the linear combination of only a few basic temporal patterns accounts for most of the electromyography (EMG) data measured during locomotion and suggested that the central pattern generator (CPG) produces a few pulses for one gait cycle that are distributed to motoneurons to create motor commands
The adaptive locomotion mechanism during split-belt treadmill walking was investigated using a neuromusculoskeletal model of rats

Summary

Introduction

Locomotor adaptability in animals has been investigated using a split-belt treadmill, which has two parallel belts whose speeds are controlled independently to prepare left–right symmetric and asymmetric environments for walking[1,2,3,4,5,6,7,8,9,10]. Our working hypothesis was that resetting the onset timings of basic temporal patterns based on the sensory information, such as extension of hip flexors, contributes to adaptive split-belt treadmill walking. In the present study, simple CPG model using phase oscillators was used to more understand the locomotor adaptation mechanism from the perspective of dynamics, based on the muscle synergy hypothesis and phase resetting by sensory feedback signals from the legs. The CPG model produces motor commands by the linear combination of a few pulses and manipulates the activation timing of the pulses through phase resetting based on hip extension. Forward dynamic simulations were performed to investigate whether control of the activation timing of a few pulses through phase resetting based on hip extension induced adaptive locomotor behavior during bipedal split-belt treadmill walking. The contribution of the timing control of a few pulses by phase resetting to locomotor adaptability is discussed

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