Regulatory Mechanisms Underlying Postural Stability

这项提议的主要目的是研究中枢神经系统如何补偿在姿势反应产生过程中失去的感觉和运动输入。为了揭示与补偿适应有关的控制信号，必须研究随时间变化的响应调制。据推测，当感觉或运动功能受损时，姿势行为变得更加受限，反应选择减少。在需要有限反应行为的受限环境中，减少控制选项可能就足够了。然而，在具有多种信号的复杂环境中，反应可能不适应刺激环境。具体地说，在随机和可预测的线性平移过程中，健康受试者和那些迷路丢失和小脑损伤的受试者在黑暗中坐着时，躯干受约束或不受约束时，头部、颈部和躯干之间的适应性变化将被检查。响应运动学（头部和躯干角速度和肌肉激活）将用快速傅里叶变换的重叠窗口进行分析，以检查时频行为。将计算压力中心和质量中心，以估计适应过程的有效刚度和阻尼特性。为了研究惯性场如何改变时频特性，将加重头部或加强颈部。统计分析将确定受损的中枢神经系统是否对这些变化表现出相同的适应速度。我们将使用增量刚度和阻尼矩阵的递归非线性系统识别来量化这些控制参数。生理控制变量将使用本实验室开发的头部和颈部的同胚计算模型进行预测。利用虚拟环境，动态视觉输入对时变适应过程的贡献以及动态视野对头颈躯干响应的相对影响也将被检查。假设迷路丢失的患者会选择单一的增加僵硬的控制策略，从而干扰头部和躯干的协调过程。患有小脑病变的患者将无法调节，因此他们的反应要么过度，要么被抑制。迷路丢失和小脑控制对体位定向和稳定性的功能影响尚不明确。适应过程的量化应该揭示其在自然、动态环境中的有效性，并可能提出姿态不稳定的修复方法。

The broad aim of this proposal is to examine how the CNS compensates for the loss of sensory and motor inputs during the production of postural reactions. In order to reveal the control signals involved in compensatory adaptation, response modulation over time must be examined. It is hypothesized that when sensory or motor function is impaired, postural behaviors become more constrained and response options decrease. Reduced control options may be sufficient in a constrained environment that requires a limited repertoire of response behaviors. In a complex environment with multiple signals, however, responses may not be adaptive to stimulus context. Specifically, adaptive modifications between the head, neck, and trunk during random and predictable linear translations in healthy subjects and in those with labyrinthine loss and cerebellar damage while seated in the dark with and without the trunk constrained will be examined. Response kinematics (head and trunk angular velocity and muscle activations) will be analyzed with overlapping windows of Fast Fourier Transforms to examine the time-frequency behavior. Center of pressure and center of mass will be calculated to estimate effective stiffness and damping characteristics of the adaptation process. The head will be weighted or the neck stiffened to investigate how an inertial field modifies the time- frequency behaviors. Statistical analyses will determine whether a damaged CNS exhibits the same rate of adaptation to these changes. We will quantify these control parameters using a recursive nonlinear system identification of incremental stiffness and damping matrices. Physiological control variables will be predicted using the homeomorphic computational model of the head and neck developed in this lab. Using a virtual environment, the contribution of dynamic visual inputs to the time varying adaptation process and the relative influence of a dynamic visual field on the head-neck-trunk responses will also be examined. It is hypothesized that patients with labyrinthine loss will select a single control strategy of increasing stiffness, thereby interfering with the coordinative process between the head and trunk. Patients with cerebellar lesions will be unable to modulate so that their responses are either excessive or suppressed. The functional consequences of labyrinthine loss and cerebellar control on postural orientation and stability are not well defined. Quantification of the adaptation process should reveal its effectiveness in a natural, dynamic environment and may suggest methods for remediation of postural instability.