POSTURAL STABILIZATION AND VISUAL ORIENTATION IN ELDERLY

该项目的总体目标是确定通常用于头部稳定的机制，包括来自前庭耳石和耳管的信号及其与被动机械特性的相互作用，如何被自愿视觉处理任务的同时需求所改变。具体来说，本研究探讨了老年人和年轻人在同时面对视觉敏锐度和姿势稳定任务时如何协调他们的头部和躯干运动。我们假设，如果视觉控制头部的位置，就不应该有冲突——头部总是会稳定视野。但是，如果头部是响应提升力量的整个身体协同作用的一部分，那么可能不得不做出选择。当头部的稳定受到空间（即视觉方向）和躯干（即身体方向）的调节时，我们预计姿势稳定动作的神经和生物力学特征会有所不同。在前-后平移和侧平移时的反应，即在功能运动中表现出显著力量的运动平面，将在躯干固定或自由运动时坐着和站立时进行检查。受试者将被呈现一个立体视野，其中包含一个稳定的焦点图像，一个与躯干旋转同相位的图像，以及一个与躯干非同相位移动的视觉图像。将使用平滑的位置斜坡、正弦波和PRBS刺激，并允许我们推导响应的时域和频域特性。考虑到头部-视觉目标和头-身体稳定可以毫无问题地一起工作，我们预计会发现，特别是在老年人中，存在一些限制（例如机械），需要做出一些决定，以牺牲另一个功能为代价来支持一个功能。将分析颈部和躯干肌肉的空间组织和反应幅度，以表征神经反应策略。将头颈部位置反射控制与下降控制和系统力学相结合的模型将用于帮助分析和预测姿势控制机制。阐明姿势稳定的机制之间的关系有助于临床医生评估跌倒和平衡障碍的原因，并有助于改善老年人和中枢神经系统缺陷患者的治疗干预措施。

The overall goal of this project is to determine how the mechanisms normally used for head stabilization, including signals from vestibular otoliths and canals and their interaction with passive mechanical properties, are modified by the simultaneous demands of a voluntary visual processing task. Specifically, this proposal explores how elderly and young adults coordinate their head and trunk movements when confronted with simultaneous visual acuity and postural stabilization tasks. We hypothesize that if vision controls head position, there should be no conflict - the head will always work to stabilize the visual field. But, if the head is part of a whole body synergy in response to ascending forces, a choice might have to be made. We would expect different neural and biomechanical characteristics of postural stabilizing actions when stabilization of the head is regulated with respect to space (i.e., visual orientation) versus with respect to trunk (i.e., body orientation). Responses during anterior- posterior and lateral translations, the planes of motion where significant power has been demonstrated during functional locomotion, will be examined in subjects seated with the trunk fixed or free to move and when standing. Subjects will be presented with a stereo visual field containing a stable focal image, an image that is in phase with the rotation of the trunk, and a visual image that moves out of phase with the trunk. Smoothed position ramps, sinusoids, and PRBS stimuli will be used and will permit us to derive both time and frequency domain characteristics of the response. Given that head4o-visual target and head-to-body stabilization can operate without problems together, we expect-to find, particularly in the elderly, that there are limits (e.g. mechanical) which call for some decision to favor one function at the cost of the other. Both the spatial organization and response magnitudes of the neck and trunk muscles will be analyzed to characterize the neural response strategies. Models that incorporate reflex control of head and neck position with descending controls and system mechanics will be used to assist in the analysis and prediction of postural control mechanisms. Clarification of relations between the mechanisms responsible for postural stabilization should assist clinicians in evaluating the causes of falling and balance disturbances, and should improve therapeutic interventions applied both to the elderly and to patients with central nervous system deficit.