Perturbation parameters associated with nonlinear responses of the head at small amplitudes
Perturbation parameters associated with nonlinear responses of the head at small amplitudes
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DOI：
10.1063/1.1938347
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发表时间：
2005-06-01
期刊：
影响因子：
2.9
通讯作者：
Keshner, EA
中科院分区：
文献类型：
--
作者：
Gurses, S;Dhaher, Y;Keshner, EA
头颈部系统在其控制和响应特性方面具有多个自由度，但通常被建模为单关节机械系统。在这项研究中，我们试图量化的扰动参数，将引起在一个单一的自由度的神经机械系统在小振幅和扰动速度的非线性响应。12名坐在线性滑轨上的健康年轻人随机接受前后正弦平移，峰值位移为+/- 15 mm和+/- 25 mm，频率为0.81、1.76和2.25 Hz。头部角速度和角位置数据进行了检查，使用非线性相平面分析。计算了相平面的庞加莱截面和李雅普诺夫指数，以衡量系统动力学的发散（混沌行为）或收敛（稳定行为）。头部角位置和速度在整个相位图的变异性进行了比较，庞加莱部分量化时空不规则性。多个平衡点和正的李雅普诺夫指数显示在0.81 Hz的两个振幅，而在1.76和2.25 Hz的响应表现出周期性振荡，群集相点，和负的李雅普诺夫指数的混沌行为。然而，受试者间的变异性在最低频率时增加，少数受试者在所有频率下都表现出混乱的行为。采用具有位置和速度阈值非线性的倒立摆作为头颈部的简化模型。与模型的模拟结果在实验数据中观察到的功能相似。我们的主要发现是，增加扰动振幅有稳定的影响，在整个频率的行为。在最低刺激频率下观察到的非线性行为可能归因于多个感觉输入之间的控制波动。虽然这项研究还没有最终指出任何单一的机制，负责观察到的反应，它揭示了进一步调查的明确方向。为了检查改变感觉方式是否会引起这里观察到的非线性行为的显著变化，需要针对具有某种感觉缺陷的患者群体进行进一步的实验。(C)2005年美国物理学会。
The head-neck system has multiple degrees of freedom in both its control and response characteristics, but is often modeled as a single joint mechanical system. In this study, we have attempted to quantify the perturbation parameters that would elicit nonlinear responses in a single degree-of-freedom neuromechanical system at small amplitudes and velocities of perturbation. Twelve healthy young adults seated on a linear sled randomly received anterior-posterior sinusoidal translations with +/- 15 mm and +/- 25 mm peak displacements at 0.81, 1.76, and 2.25 Hz. Head angular velocity and angular position data were examined using a nonlinear phase-plane analysis. Poincare sections of the phase plane were computed and Lyapunov exponents calculated to measure divergence (chaotic behavior) or convergence (stable behavior) of system dynamics. Variability of head angular position and velocity across the entire phase plot was compared to that of the Poincare sections to quantify spatial-temporal irregularity. Multiple equilibrium points and positive Lyapunov exponents revealed chaotic behavior at 0.81 Hz at both amplitudes whereas responses at 1.76 and 2.25 Hz exhibited periodic oscillations, clustered phase points, and negative Lyapunov exponents. However, intersubject variability increased at the lowest frequency and a few subjects presented chaotic behavior at all frequencies. An inverted pendulum with position and velocity threshold nonlinearity was adopted as a simplistic model of the head and neck. Simulations with the model resulted in features similar to those observed in the experimental data. Our principal finding was that increasing the perturbation amplitude had a stabilizing effect on the behavior across frequencies. Nonlinear behaviors observed at the lowest stimulus frequency might be attributed to fluctuations in control between the multiple sensory inputs. Although this study has not conclusively pointed toward any single mechanism as responsible for the responses observed, it has revealed clear directions for further investigation. To examine if changing the sensory modalities would elicit a significant change in the nonlinear behaviors observed here, further experiments that target a patient population with some sort of sensory deficit are warranted. (C) 2005 American Institute of Physics.