Rougier Patrice R, Fleury Paul-Henri, Tollenaere Baptiste
Laboratoire Interdisciplinaire de Biologie de la Motricité, EA 7424, Université de Savoie-Mont-Blanc, Domaine Scientifique de Savoie-Technolac, 73376, Le Bourget du Lac cedex, France.
Exp Brain Res. 2019 Feb;237(2):547-555. doi: 10.1007/s00221-018-5433-x. Epub 2018 Nov 27.
Additional visual feedback (VFB) is a technique allowing improved postural stability in young healthy individuals despite an increased muscular activity, the two trends being assessed through center-of-gravity (CG) and differences between CG and center-of-pressure (CP) movements (CP-CG), respectively. These two opposing effects are likely explained by the respective contribution of automatic and voluntary controls and in turn the neural circuits involved. To specify these specific contributions, a dual-task protocol was set up, consisting in adding to VFB a navigation task performed at the maximum cognitive capacities of the subjects who were evaluated beforehand. Overall, the protocol comprises six conditions: three visual tasks (eyes open without VFB, VFB based on body-weight distribution, VFB based on CP displacements) associated with or without a cognitive task. Variances of CP-CG and CG movements, along the mediolateral (ML) and anteroposterior (AP) axes, and parameters from fractional Brownian motion modeling (transition point coordinates and scaling regimes to assess the level of deterministic or stochastic activity) were used to assess the postural behaviors. The results show that during VFB, the dual tasks protocol infers a decreased contribution of deterministic activity in CP-CG movements, inducing decreased variances, and alters the correction of the CG over the longest Δt but nonetheless without changing CG variances. Disturbing the subject's attention during the VFB condition induces decreased CP-CG and CG movements along the ML and AP axes, respectively. These data demonstrate the high level of attention induced by VFB protocols. If the tonic postural activity, expressed through CP-CG movements, decreases whatever VFB condition along both the ML and AP axes, the effects on CG movement appear to be mostly related to the additional information (BW or CP) provided. Overall, if too much voluntary control in upright stance maintenance is detrimental for the magnitudes of the CP-CG movements, it appears beneficial for those of the CG movements. By emphasizing the role of automatic and voluntary controls in VFB protocols, these insights document the neural circuits involved in such protocols and specify their conditions of use.
额外视觉反馈（VFB）是一种技术，它能使年轻健康个体在肌肉活动增加的情况下提高姿势稳定性，这两种趋势分别通过重心（CG）以及重心与压力中心（CP）运动之间的差异（CP-CG）来评估。这两种相反的效应可能分别由自动控制和自主控制的各自贡献以及相关神经回路来解释。为了明确这些具体贡献，设置了一个双任务方案，即在VFB的基础上增加一项导航任务，该任务以事先评估过的受试者的最大认知能力来执行。总体而言，该方案包括六种情况：三个视觉任务（睁眼无VFB、基于体重分布的VFB、基于CP位移的VFB），分别与认知任务相关或不相关。CP-CG和CG运动沿内外侧（ML）和前后（AP）轴的方差，以及分数布朗运动建模的参数（过渡点坐标和缩放比例以评估确定性或随机活动水平）用于评估姿势行为。结果表明，在VFB期间，双任务方案推断出CP-CG运动中确定性活动的贡献减少，导致方差减小，并在最长的Δt内改变了CG的校正，但CG方差不变。在VFB条件下干扰受试者的注意力会分别导致沿ML和AP轴的CP-CG和CG运动减少。这些数据证明了VFB方案引起的高度注意力。如果通过CP-CG运动表现出的紧张姿势活动在任何VFB条件下沿ML和AP轴都降低，那么对CG运动的影响似乎主要与提供的额外信息（体重或CP）有关。总体而言，如果在维持直立姿势时过多的自主控制对CP-CG运动的幅度不利，那么对CG运动的幅度似乎是有益的。通过强调自动控制和自主控制在VFB方案中的作用，这些见解记录了此类方案中涉及的神经回路并明确了其使用条件。
