Increased gravitational force reveals the mechanical, resonant nature of physiological tremor.
Increased gravitational force reveals the mechanical, resonant nature of physiological tremor.
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DOI：
10.1113/jp270464
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发表时间：
2015-10-01
期刊：
影响因子：
--
通讯作者：
Reynolds RF
中科院分区：
文献类型：
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作者：
Lakie M;Vernooij CA;Osler CJ;Stevenson AT;Scott JP;Reynolds RF
生理性手震颤在6和12 Hz之间具有明显的峰值，这归因于神经和共振原因。通过向肢体添加惯性质量来降低震颤频率通常被用作识别共振分量的方法。然而，给肢体增加质量也不可避免地增加了维持肢体对抗重力的位置所需的肌肉力量，因此报告了模棱两可的结果。在这里，我们测量手震颤在不同水平的重力场强度使用人体离心机，从而增加所需的肌肉力量，以保持肢体的位置，而不改变肢体的惯性。通过比较增加的质量（惯性+力）与单独增加的力在手加速度的效果，我们得出结论，震颤频率几乎可以完全解释由共振机械系统。人的生理性手震颤具有共振成分。这一点的证明是，它的频率可以通过增加质量来修改。然而，增加质量也增加了必须支撑的载荷。必要的力量需要肌肉收缩，这将改变运动输出，并可能增加肢体僵硬。增加的刚度将部分抵消增加的质量的影响，这可能导致错误的结论，即共振以外的因素参与确定震颤频率。使用人体离心机来增加从头到脚的重力场强度，我们能够通过增加力而不改变质量来控制增加的努力。这表明，根据共振机制，人手震颤的峰值频率可预测99%。我们要问的是，生理震颤的峰值频率能揭示神经系统的运作情况。
Physiological hand tremor has a clear peak between 6 and 12 Hz, which has been attributed to both neural and resonant causes. A reduction in tremor frequency produced by adding an inertial mass to the limb has usually been taken as a method to identify the resonant component. However, adding mass to a limb also inevitably increases the muscular force required to maintain the limb's position against gravity, so ambiguous results have been reported. Here we measure hand tremor at different levels of gravitational field strength using a human centrifuge, thereby increasing the required muscular force to preserve limb position without changing the limb's inertia. By comparing the effect of added mass (inertia + force) versus solely added force upon hand acceleration, we conclude that tremor frequency can be almost completely explained by a resonant mechanical system. Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head‐to‐foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system.