Lim Shannon B, Cleworth Taylor W, Horslen Brian C, Blouin Jean-Sébastien, Inglis J Timothy, Carpenter Mark G
School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
The Institute for Computing, Information and Cognitive Systems, University of British Columbia, Vancouver, British Columbia, Canada.
J Neurophysiol. 2017 Feb 1;117(2):604-611. doi: 10.1152/jn.00712.2016. Epub 2016 Nov 9.
Standing balance is significantly influenced by postural threat. While this effect has been well established, the underlying mechanisms of the effect are less understood. The involvement of the vestibular system is under current debate, and recent studies that investigated the effects of height-induced postural threat on vestibular-evoked responses provide conflicting results based on kinetic (Horslen BC, Dakin CJ, Inglis JT, Blouin JS, Carpenter MG. J Physiol 592: 3671-3685, 2014) and kinematic (Osler CJ, Tersteeg MC, Reynolds RF, Loram ID. Eur J Neurosci 38: 3239-3247, 2013) data. We examined the effect of threat of perturbation, a different form of postural threat, on coupling (cross-correlation, coherence, and gain) of the vestibulo-muscular relationship in 25 participants who maintained standing balance. In the "No-Threat" conditions, participants stood quietly on a stable surface. In the "Threat" condition, participants' balance was threatened with unpredictable mediolateral support surface tilts. Quiet standing immediately before the surface tilts was compared to an equivalent time from the No-Threat conditions. Surface EMG was recorded from bilateral trunk, hip, and leg muscles. Hip and leg muscles exhibited significant increases in peak cross-correlation amplitudes, coherence, and gain (1.23-2.66×) in the Threat condition compared with No-Threat conditions, and significant correlations were observed between threat-related changes in physiological arousal and medium-latency peak cross-correlation amplitude in medial gastrocnemius (r = 0.408) muscles. These findings show a clear threat effect on vestibular-evoked responses in muscles in the lower body, with less robust effects of threat on trunk muscles. Combined with previous work, the present results can provide insight into observed changes during balance control in threatening situations.
NEW & NOTEWORTHY: This is the first study to show increases in vestibular-evoked responses of the lower body muscles under conditions of increased threat of postural perturbation. While robust findings were observed in hip and leg muscles, less consistent results were found in muscles of the trunk. The present findings provide further support in the ongoing debate for arguments that vestibular-evoked balance responses are influenced by fear and anxiety and explain previous threat-related changes in balance.
站立平衡受姿势威胁的显著影响。虽然这种影响已得到充分证实，但其潜在机制尚不太清楚。前庭系统的参与目前存在争议，最近研究高度诱发的姿势威胁对前庭诱发反应影响的研究，基于动力学（霍尔斯伦BC、达金CJ、英格利斯JT、布卢瓦因JS、卡彭特MG。《生理学杂志》592：3671 - 3685，2014）和运动学（奥斯勒CJ、特斯泰格MC、雷诺兹RF、洛拉姆ID。《欧洲神经科学杂志》38：3239 - 3247，2013）数据得出了相互矛盾的结果。我们在25名保持站立平衡的参与者中，研究了一种不同形式的姿势威胁——扰动威胁，对前庭 - 肌肉关系耦合（互相关、相干性和增益）的影响。在“无威胁”条件下，参与者安静地站在稳定表面上。在“威胁”条件下，参与者的平衡受到不可预测的内外侧支撑表面倾斜的威胁。将表面倾斜前的安静站立与无威胁条件下的相同时间进行比较。从双侧躯干、臀部和腿部肌肉记录表面肌电图。与无威胁条件相比，在威胁条件下，臀部和腿部肌肉的峰值互相关幅度、相干性和增益显著增加（1.23 - 2.66倍），并且在内侧腓肠肌中观察到生理唤醒的威胁相关变化与中潜伏期峰值互相关幅度之间存在显著相关性（r = 0.408）。这些发现表明姿势威胁对下半身肌肉的前庭诱发反应有明显影响，而对躯干肌肉的威胁影响较弱。结合先前的研究工作，本研究结果可以为理解在威胁情况下平衡控制过程中观察到的变化提供见解。
这是第一项表明在姿势扰动威胁增加的情况下，下半身肌肉的前庭诱发反应增加的研究。虽然在臀部和腿部肌肉中观察到了有力的结果，但在躯干肌肉中发现的结果不太一致。本研究结果为正在进行的关于前庭诱发平衡反应受恐惧和焦虑影响的争论提供了进一步支持，并解释了先前与威胁相关的平衡变化。
