Vestibular control of head movements

描述（由申请人提供）：眼睛和头部的运动必须协调，以重新定向视线（“凝视方向”），并减少头部在空间中移动时穿过视网膜的图像运动。由于这些目标在本质上是相互冲突的，因此所需的协调模式是复杂的。在以往的研究中，眼球运动常用于研究前庭反应（前庭-眼反射或VOR）；实验在头部受限的受试者中进行被动旋转刺激。然而，这种方法无法评估眼睛、头部和身体运动之间自然发生的相互作用，因此在阐明前庭系统在眼-头协调中的作用方面受到限制。在这项研究中，头部不受约束，我们比较了被动全身旋转（PWBR）和自我产生（主动）头部运动的反应。PWBR允许研究眼睛和头部运动，这些运动协同促进凝视稳定性。相反，在自我产生的头部运动中，补偿性头部运动将反对动物重新定向视线的意图。因此，前庭系统在主动头部运动中的作用必须与其在与PWBR相关的代偿运动中的作用区分开来。本研究的目的是了解前庭系统在由PWBR或自我产生的头部运动引起的不同的眼-头协调模式中的贡献。这一目标将在两个具体目标中实现：(1)确定在PWBR期间前庭降输入对颈椎运动神经元的作用；(2)确定在自生成头部运动与PWBR条件下前庭降输入对颈椎运动神经元的作用。弱前庭电刺激（GVS）将被用作控制前庭流出的实验干预，因为这种方法已被证明可以选择性地抑制或增强来自不规则传入的前庭信号，这些传入可能优先促进前庭脊髓信号。这些目的将验证前庭下行输入在PWBR期间产生代偿性头部运动反应中发挥重要作用，但在主动头部运动期间可能被抑制的假设。颈部运动神经元的活动将独立于头部运动进行评估，通过测量与代偿性或主动头部转动有关的选定颈部肌肉的肌电图活动。

DESCRIPTION (provided by applicant): Eye and head movements must be coordinated to redirect the line of sight ("gaze direction") and to reduce image motion across the retina as the head moves through space. Because these goals are inherently in conflict, the required pattern of coordination is complex. In previous research, eye movements were often used to study vestibular responses (vestibulo-ocular reflex or VOR); experiments were performed in head-restrained subjects undergoing passive rotational stimuli. However, this approach is unable to assess the interplay that naturally occurs between movements of the eye, head, and body and thus is limited in its ability to illuminate the role of the vestibular system in eye-head coordination. In this study, the head is unrestrained and we compare responses to passive whole body rotations (PWBR) and self-generated (active) head movements. PWBR allows for the study of eye and head movements that synergistically contribute to gaze stability. In contrast, during self-generated head movements, compensatory head movements would oppose the animal's intention to redirect the line of sight. Thus, the role of the vestibular system during active head movements must be distinguished from its role during compensatory movements associated with PWBR. The goal of this research is to understand the contribution of the vestibular system during the differing patterns of eye-head coordination provoked by PWBR or self-generated head movements. This goal will be achieved in two specific aims: (1) determine the role of descending vestibular inputs to cervical motoneurons during PWBR and (2) determine the role of descending vestibular inputs to cervical motoneurons during self-generated head movements versus the PWBR condition. Weak galvanic vestibular stimulation (GVS) will be used as an experimental intervention to manipulate the vestibular outflow since this method has been shown to selectively suppress or enhance the vestibular signal from irregular afferents that may preferentially contribute to the vestibulospinal signal. These aims will test the hypothesis that descending vestibular inputs play a significant role in producing the compensatory head movement response during PWBR but may be suppressed during active head movements. Cervical motoneuron activity will be assessed independently of head movement by measuring EMG activity from selected neck muscles involved in the compensatory or active head turns. PUBLIC HEALTH RELEVANCE: Diagnostic tests of inner ear balance mechanisms rely heavily on measurement of eye movements. However, balance is naturally the result of a coordinated interaction of eye, head and body movements; thus consideration of only one of these components may lead to an incomplete understanding of the cause of an inner ear medical problem. This research will be instrumental in the development of novel approaches to clinical tests of inner ear dysfunction as well as its improved treatments.