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Front. Hum. Neurosci. | doi: 10.3389/fnhum.2018.00068

Corticospinal excitability is modulated as a function of postural perturbation predictability

 Kimiya FUJIO1, 2,  Hiroki OBATA3*,  Taku Kitamura2, Noritaka KAWASHIMA2 and Kimitaka NAKAZAWA4
  • 1Department of Rehabilitation Science, Chiba Prefectural University of Health Sciences, Japan
  • 2Department of Rehabilitation for the Movement Functions, National Rehabilitation Center for Persons with Disabilities, Japan
  • 3Department of Humanities and Social Sciences, Kyushu Institute of Technology, Japan
  • 4Graduate School of Arts and Sciences, The University of Tokyo, Japan

Abstract
Recent studies demonstrated that the corticospinal pathway is one of the key nodes for the feedback control of human standing and that the excitability is flexibly changed according to the current state of posture. However, it has been unclear whether this pathway is also involved in a predictive control of human standing. Here, we investigated whether the corticospinal excitability of the soleus (SOL) and tibialis anterior (TA) muscles during standing would be modulated anticipatorily when perturbation was impending. We measured the motor-evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) over the motor cortex at six stimulus intensities. Three experimental conditions were set depending on predictabilities about perturbation occurrence and onset: No perturbation, No Cue, and Cue conditions. In the Cue condition, an acoustic signal was given as timing information of perturbation. The slope of the stimulus-response relation curve revealed that the TA-MEP was enhanced when postural perturbation was expected compared to when the perturbation was not expected (No perturbation vs. No Cue, 0.023±0.004 vs. 0.042±0.007; No perturbation vs. Cue, 0.023±0.004 vs. 0.050±0.009; Bonferroni correction, p=0.01, respectively). In addition, two-way ANOVA (intensity × condition) revealed the main effect of condition (F1,13=6.31, p=0.03) but not intensity and interaction when the MEP amplitude of the Cue and No Cue conditions was normalized by that in No perturbation, suggesting the enhancement more apparent when timing information was given. The SOL-MEP was not modulated even when perturbation was expected, but it slightly reduced due to the timing information. The results of an additional experiment confirmed that the acoustic cue by itself did not affect the TA- and SOL-MEPs. Our findings suggest that a prediction of a future state of standing balance modulates the corticospinal excitability in the TA, and that the additional timing information facilitates this modulation. The corticospinal pathway thus appears to be involved in mechanisms of the predictive control as well as feedback control of standing posture.

Keywords: Posture, the cotricospinal pathway, prediction, Tibialis anterior muscle, Transcranial Magnetic Stimulation

Received: 26 Oct 2017; Accepted: 06 Feb 2018.

Edited by:

Klaus Gramann, Technische Universität Berlin, Germany

Reviewed by:

Fiorenzo Artoni, Sant'Anna School of Advanced Studies, Italy
Craig Tokuno, Brock University, Canada  

Copyright: © 2018 FUJIO, OBATA, Kitamura, KAWASHIMA and NAKAZAWA. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: PhD. Hiroki OBATA, Kyushu Institute of Technology, Department of Humanities and Social Sciences, 1-1 Sensui-cho, Kitakyushu, 804-8550, Fukuoka, Japan, hirokiobata@gmail.com