The Effects of Temporal and Spatial Predictions on Stretch Reflexes of Ankle Flexor and Extensor Muscles While Standing.

Kimiya Fujio,Hiroki Obata,Noritaka Kawashima,Kimitaka Nakazawa,Mikhail A Lebedev

doi:10.1371/journal.pone.0158721

Kimiya Fujio, Hiroki Obata + Show 3 more

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https://doi.org/10.1371/journal.pone.0158721

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Abstract

The purpose of the present study was to investigate how stretch reflex (SR) responses in the ankle extensor (soleus: SOL) and flexor (tibialis anterior: TA) muscles would be modulated with temporal and/or spatial predictions of external perturbations and whether their effects are specific to the standing posture. SR responses in the SOL/TA were elicited by imposing quick ankle toes-up/toes-down rotations while standing upright and in the supine position. We designed four experimental conditions based on pre-information about perturbations: no information (No Cue), the timing of the perturbation onset (TIM), the direction of the perturbation (DIR), and both the timing and direction of the perturbation (TIM/DIR). Each condition was separated and its order was counterbalanced. In the SR of TA evoked by toes-down rotation, integrated electromyography activities of the late component were significantly reduced in the TIM and TIM/DIR conditions as compared with those in the No Cue and DIR conditions. The occurrence rate of late SR components that reflects how often the reflex response was observed was also lower in the TIM and TIM/DIR conditions as compared with that in the No Cue and DIR conditions. On the other hand, no significant changes were seen among the four conditions in the early SR component in the TA and both SR components in the SOL. The same results in the occurrence rate were found in the supine position. The present results suggest (1) only temporal predictions have a remarkable effect on the SR excitability of the TA, and (2) this effect is independent of posture.

Highlights

Postural responses to sudden external perturbations are important for preventing falls in the course of daily living
Effect of temporal and spatial prediction on stretch reflexes (SR) responses while standing The SR of the tibialis anterior muscle (TA) elicited by toes-down rotation and that of the SOL elicited by toes-up rotation were analyzed
Because there were no detectable differences between EMG responses recorded of legs on both sides and the kinematic data was recorded from the left side, only the result of the left side was shown in this study

Summary

Introduction

Postural responses to sudden external perturbations are important for preventing falls in the course of daily living. Once standing balance has been disturbed, stretch reflexes (SR) and subsequent correcting responses are initiated approximately 40–120 ms after the perturbation onset. SRs of the ankle muscles are generally divided into three components, depending on the latencies following perturbation. The short-latency response (SLR) is regarded as a PLOS ONE | DOI:10.1371/journal.pone.0158721. The later components, medium- (MLR) and longlatency responses (LLR), are known to be modified more flexibly by a subject’s preparatory states, such as prior experience [2], threat of falling [3], intention to accomplish a task [4, 5], and postural orientation [6, 7]

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