Adaptation mechanism of interlimb coordination in human split-belt treadmill walking through learning of foot contact timing: a robotics study.

Soichiro Fujiki,Kazuo Tsuchiya,Tetsuro Funato,Shinya Aoi,Nozomi Tomita,Kei Senda

doi:10.1098/rsif.2015.0542

Abstract

Human walking behaviour adaptation strategies have previously been examined using split-belt treadmills, which have two parallel independently controlled belts. In such human split-belt treadmill walking, two types of adaptations have been identified: early and late. Early-type adaptations appear as rapid changes in interlimb and intralimb coordination activities when the belt speeds of the treadmill change between tied (same speed for both belts) and split-belt (different speeds for each belt) configurations. By contrast, late-type adaptations occur after the early-type adaptations as a gradual change and only involve interlimb coordination. Furthermore, interlimb coordination shows after-effects that are related to these adaptations. It has been suggested that these adaptations are governed primarily by the spinal cord and cerebellum, but the underlying mechanism remains unclear. Because various physiological findings suggest that foot contact timing is crucial to adaptive locomotion, this paper reports on the development of a two-layered control model for walking composed of spinal and cerebellar models, and on its use as the focus of our control model. The spinal model generates rhythmic motor commands using an oscillator network based on a central pattern generator and modulates the commands formulated in immediate response to foot contact, while the cerebellar model modifies motor commands through learning based on error information related to differences between the predicted and actual foot contact timings of each leg. We investigated adaptive behaviour and its mechanism by split-belt treadmill walking experiments using both computer simulations and an experimental bipedal robot. Our results showed that the robot exhibited rapid changes in interlimb and intralimb coordination that were similar to the early-type adaptations observed in humans. In addition, despite the lack of direct interlimb coordination control, gradual changes and after-effects in the interlimb coordination appeared in a manner that was similar to the late-type adaptations and after-effects observed in humans. The adaptation results of the robot were then evaluated in comparison with human split-belt treadmill walking, and the adaptation mechanism was clarified from a dynamic viewpoint.

Highlights

Human beings walk adaptively in various environments by generating appropriate motor commands in their neural systems
In our previous work [20], we developed a simple spinal cord locomotion control model for use as a walking neural control model based on the physiological concept of a central pattern generator (CPG) and sensory reflexes related to foot contact
We developed a locomotion control model composed of two layers; a spinal model that produces motor commands to manipulate the robot based on CPG and sensory reflex, and a cerebellum model that modulates motor commands through learning

Summary

Introduction

Human beings walk adaptively in various environments by generating appropriate motor commands in their neural systems. As walking continues using this two-speed belt condition, locomotion parameters related to interlimb coordination, such as the relative phase and COP profile, gradually change and show a behaviour trend towards that coinciding with the baseline state, whereas locomotion parameters related to the intralimb coordination, such as the duty factor, do not show further adaptation. This gradual change in the interlimb coordination is called late adaptation.

Methods

Results

Conclusion