School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK.
Eur J Neurosci. 2013 Oct;38(8):3239-47. doi: 10.1111/ejn.12336. Epub 2013 Aug 18.
Circumstances may render the consequence of falling quite severe, thus maximising the motivation to control postural sway. This commonly occurs when exposed to height and may result from the interaction of many factors, including fear, arousal, sensory information and perception. Here, we examined human vestibular-evoked balance responses during exposure to a highly threatening postural context. Nine subjects stood with eyes closed on a narrow walkway elevated 3.85 m above ground level. This evoked an altered psycho-physiological state, demonstrated by a twofold increase in skin conductance. Balance responses were then evoked by galvanic vestibular stimulation. The sway response, which comprised a whole-body lean in the direction of the edge of the walkway, was significantly and substantially attenuated after ~800 ms. This demonstrates that a strong reason to modify the balance control strategy was created and subjects were highly motivated to minimise sway. Despite this, the initial response remained unchanged. This suggests little effect on the feedforward settings of the nervous system responsible for coupling pure vestibular input to functional motor output. The much stronger, later effect can be attributed to an integration of balance-relevant sensory feedback once the body was in motion. These results demonstrate that the feedforward and feedback components of a vestibular-evoked balance response are differently affected by postural threat. Although a fear of falling has previously been linked with instability and even falling itself, our findings suggest that this relationship is not attributable to changes in the feedforward vestibular control of balance.
环境因素可能会使跌倒的后果非常严重，从而最大限度地提高控制姿势摆动的动机。当暴露在高处时，这种情况通常会发生，并且可能是由许多因素相互作用引起的，包括恐惧、兴奋、感觉信息和感知。在这里，我们研究了人类在暴露于高度威胁的姿势环境中时的前庭诱发平衡反应。九名受试者闭着眼睛站在高出地面 3.85 米的狭窄走道上。这会引起心理生理状态的改变，表现为皮肤电导率增加一倍。然后通过电前庭刺激引发平衡反应。摇摆反应包括整个身体向走道边缘倾斜，在大约 800 毫秒后明显且大大减弱。这表明已经创造了一个强烈的理由来改变平衡控制策略，并且受试者非常有动力来最小化摇摆。尽管如此，初始反应保持不变。这表明对负责将纯前庭输入与功能性运动输出耦合的神经系统的前馈设置几乎没有影响。更强、更晚的影响可以归因于一旦身体开始运动，与平衡相关的感觉反馈的整合。这些结果表明，前庭诱发平衡反应的前馈和反馈成分受到姿势威胁的不同影响。尽管以前有人将跌倒恐惧与不稳定甚至跌倒本身联系起来，但我们的发现表明，这种关系并不是由于平衡的前馈前庭控制的变化引起的。
