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（“注视方向”），并减少头部在空间中移动时视网膜上的图像运动。由于这些目标本身就相互冲突，所需的协调模式是复杂的。在以前的研究中，眼球运动经常被用来研究前庭反应（前庭眼反射或VOR）;实验是在头部受限的受试者中进行的，这些受试者接受被动旋转刺激。然而，这种方法无法评估眼睛、头部和身体的运动之间自然发生的相互作用，因此其阐明前庭系统在眼-头协调中的作用的能力有限。在这项研究中，头部是不受限制的，我们比较被动全身旋转（PWBR）和自发（主动）头部运动的反应。PWBR允许研究眼睛和头部运动，协同有助于凝视稳定性。相反，在自发的头部运动过程中，补偿性头部运动会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的贡献，在不同的模式的眼头协调引起的PWBR或自发的头部运动。这一目标将通过两个具体目标来实现：（1）确定PWBR期间下行前庭输入对颈运动神经元的作用，以及（2）确定与PWBR条件相比，自发头部运动期间下行前庭输入对颈运动神经元的作用。弱电流前庭刺激（GVS）将被用作一种实验干预来操纵前庭流出，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，这些传入可能优先有助于前庭脊髓信号。这些目标将测试这一假设，即下行前庭输入在PWBR期间产生补偿性头部运动反应中起重要作用，但在主动头部运动期间可能受到抑制。通过测量参与代偿性或主动头部转动的选定颈部肌肉的EMG活动，独立于头部运动评估颈部运动神经元活动。 公共卫生相关性：内耳平衡机制的诊断测试在很大程度上依赖于眼球运动的测量。然而，平衡自然是眼睛，头部和身体运动协调相互作用的结果;因此，仅考虑这些组件中的一个可能会导致对内耳医疗问题原因的不完全理解。这项研究将有助于发展新的方法，以临床测试内耳功能障碍，以及其改进的治疗。

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.