Biomedical Engineering, Daroff-Dell'Osso Laboratory, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, OH, USA.
Restor Neurol Neurosci. 2010;28(1):91-103. doi: 10.3233/RNN-2010-0507.
During locomotion, head perturbations, consisting of rotations and translations (linear movements), occur with predominant frequencies of 0.5-5.0 Hz. The vestibular reflexes act at short latency to safeguard clear vision and stable posture during locomotion. Much is known about the angular vestibulo-ocular reflex (aVOR) in response to head rotations, which depend on the semicircular canals of the vestibular labyrinth. However, the means to test reliably the linear or translational vestibulo-ocular reflex (tVOR), which depends on the otolithic organs, has only become available more recently.
We used a moving platform to translate normal human subjects vertically at frequencies similar to those occurring during locomotion, under ambient illumination.
Our findings suggested that, whereas aVOR is concerned with stabilizing images of visual targets on the retina to optimize visual acuity, tVOR seems best suited to minimize retinal image motion between objects lying in different depth planes, in order to optimize motion parallax information. We then asked whether the tVOR functioned abnormally in patients with two neurological disorders that often cause falls: progressive supranuclear palsy (PSP) and cerebellar ataxia. We found that patients with PSP cannot adjust tVOR responses appropriately during viewing of near objects, nor converge their eyes. Vestibular-evoked myogenic potentials (VEMPs), an otolith-spinal reflex, are also impaired in PSP patients. Patients with cerebellar ataxia also lack the ability to adjust tVOR for near viewing, even though they may be able to converge.
Taken together, our studies suggest that abnormal otolithic vestibular reflexes contribute to postural instability in PSP and cerebellar ataxia, and deserve further investigation.
在运动过程中，头部会发生以 0.5-5.0Hz 为主频率的旋转和平移（线性运动）扰动。前庭反射在短潜伏期起作用，以确保运动过程中清晰的视觉和稳定的姿势。人们对头部旋转时的角前庭眼反射（aVOR）了解较多，该反射取决于前庭迷路的半规管。然而，最近才出现了可靠测试依赖于耳石器官的线性或平移前庭眼反射（tVOR）的方法。
我们使用移动平台以类似于在运动过程中发生的频率，在环境照明下将正常人体受试者垂直平移。
我们的发现表明，虽然 aVOR 关注于稳定视网膜上视觉目标的图像以优化视力，但 tVOR 似乎最适合最小化位于不同深度平面的物体之间的视网膜图像运动，以优化运动视差信息。然后，我们询问了两种常导致跌倒的神经障碍患者的 tVOR 是否异常：进行性核上性麻痹（PSP）和小脑性共济失调。我们发现 PSP 患者在观看近物时无法适当调整 tVOR 反应，也无法使眼睛会聚。前庭诱发肌源性电位（VEMPs），一种耳石-脊髓反射，在 PSP 患者中也受损。小脑性共济失调患者即使能够会聚，也无法调整 tVOR 以适应近距观看。
综上所述，我们的研究表明，异常的耳石前庭反射会导致 PSP 和小脑性共济失调的姿势不稳定，值得进一步研究。
