Lacour Michel, Dosso Nadine Yavo, Heuschen Sylvie, Thiry Alain, Van Nechel Christian, Toupet Michel
Aix-Marseille University, Research Federation 3C, UMR CNRS 7260, Marseille, France.
Service ORL CCF, CHU de Treichville, Abidjan, Côte d'Ivoire.
Front Neurol. 2018 Sep 18;9:744. doi: 10.3389/fneur.2018.00744. eCollection 2018.
Chronic patients with bilateral vestibular hypofunction (BVH) complain of oscillopsia and great instability particularly when vision is excluded and on irregular surfaces. The real nature of the visual input substituting to the missing vestibular afferents and improving posture control remains however under debate. Is retinal slip involved? Do eye movements play a substantial role? The present study tends to answer this question in BVH patients by investigating their posture stability during quiet standing in four different visual conditions: total darkness, fixation of a stable space-fixed target, and pursuit of a visual target under goggles delivering visual input rate at flicker frequency inducing either slow eye movements (4.5 Hz) or saccades (1.2 Hz). Twenty one chronic BVH patients attested by both the caloric and head impulse test were examined by means of static posturography, and compared to a control group made of 21 sex-and age-matched healthy participants. The posturography data were analyzed using non-linear computation of the center of foot pressure (CoP) by means of the wavelet transform (Power Spectral Density in the visual frequency part, Postural Instability Index) and the fractional Brownian-motion analysis (stabilogram-diffusion analysis, Hausdorff fractal dimension). Results showed that posture stability was significantly deteriorated in darkness in the BVH patients compared to the healthy controls. Strong improvement of BVH patients' posture stability was observed during fixation of a visual target, pursuit with slow eye movements, and saccades, whereas the postural performance of the control group was less affected by the different visual conditions. It is concluded that BVH patients improve their posture stability by (1) using extraocular signals from eye movements (efference copy, muscle re-afferences) much more than the healthy participants, and (2) shifting more systematically than the controls to a more automatic mode of posture control when they are in dual-task conditions associating the postural task and a concomitant visuo- motor task.
双侧前庭功能减退（BVH）的慢性病患者会抱怨视振荡以及严重的不稳定性，尤其是在排除视觉因素以及处于不平整表面时。然而，替代缺失的前庭传入神经并改善姿势控制的视觉输入的真正本质仍存在争议。视网膜滑动是否参与其中？眼球运动是否起重要作用？本研究旨在通过调查21名慢性BVH患者在四种不同视觉条件下安静站立时的姿势稳定性来回答这个问题：完全黑暗、注视一个稳定的空间固定目标、以及在护目镜下追踪一个视觉目标，护目镜以闪烁频率提供视觉输入率，从而诱发慢速眼球运动（4.5赫兹）或扫视（1.2赫兹）。通过冷热试验和头部脉冲试验证实的21名慢性BVH患者通过静态姿势描记法进行检查，并与由21名年龄和性别匹配的健康参与者组成的对照组进行比较。姿势描记数据通过小波变换（视觉频率部分的功率谱密度、姿势不稳定指数）对足底压力中心（CoP）进行非线性计算以及分数布朗运动分析（稳定图扩散分析、豪斯多夫分形维数）进行分析。结果表明，与健康对照组相比，BVH患者在黑暗中的姿势稳定性明显恶化。在注视视觉目标、慢速眼球运动追踪和扫视期间，观察到BVH患者的姿势稳定性有显著改善，而对照组的姿势表现受不同视觉条件的影响较小。得出的结论是，BVH患者通过以下方式改善其姿势稳定性：（1）比健康参与者更多地利用来自眼球运动的眼外信号（传出副本、肌肉再传入）；（2）当他们处于将姿势任务与伴随的视觉运动任务相结合的双重任务条件时，比对照组更系统地转向更自动的姿势控制模式。
