Separating neural influences from peripheral mechanics: the speed-curvature relation in mechanically constrained actions
Separating neural influences from peripheral mechanics: the speed-curvature relation in mechanically constrained actions
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DOI：
10.1152/jn.00536.2019
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发表时间：
2020-05-01
影响因子：
2.5
通讯作者：
Hogan, Neville
中科院分区：
文献类型：
--
作者：
Hermus, James;Doeringer, Joseph;Hogan, Neville
虽然对不受约束的运动的研究揭示了神经控制的重要特征，但将这些见解推广到更复杂的对象操作是具有挑战性的。人类擅长与物体进行物理交互，即使这些物体引入了复杂的动力学和运动学约束。本研究考察了人类转动水平平面曲柄（半径10.29厘米）在他们的首选和三个指示的速度（视觉反馈），无论是在顺时针和逆时针方向。为了探索神经机械动力学的作用，指示的速度涵盖了很宽的范围：快（接近性能极限），中等（接近首选速度）和非常慢（呈现动态效果可忽略不计）。由于运动学约束的运动涉及重要的物理相互作用，将神经控制与生物力学的影响分开是一个挑战。为了解决这个问题，我们对交互动力学进行建模，以从观察到的力和运动学数据中“减去”外周生物力学，从而估计可能以运动表示的潜在神经行为的各个方面。我们证明了这种方法的价值：值得注意的是，一个近似椭圆形的路径出现。速度最小值与曲率最大值重合，类似于在无约束运动中所看到的，即使手以接近恒定的速度沿着恒定曲率路径移动。这些发现表明，神经控制器利用外周生物力学来简化物理交互。因此，在不受约束的运动中看到的模式持续存在，即使物理相互作用阻止它们在手部运动学中表达。速度-曲率关系的重新出现表明，这至少部分是由于强调平滑性和可预测性的神经过程。新&值得注意的是，与运动学约束的物理交互在日常行动中司空见惯。我们报告了一项关于人类转动曲柄的研究。圆形约束，施加恒定的手路径曲率，因此应该抑制由于幂律速度曲率关系广泛报道的无约束运动的手速度的变化。值得注意的是，我们发现，当周围的生物力学因素被删除，速度曲率的关系重新出现，这表明它是，至少部分，神经起源。
While the study of unconstrained movements has revealed important features of neural control, generalizing those insights to more sophisticated object manipulation is challenging. Humans excel at physical interaction with objects, even when those objects introduce complex dynamics and kinematic constraints. This study examined humans turning a horizontal planar crank (radius 10.29 cm) at their preferred and three instructed speeds (with visual feedback), both in clockwise and counterclockwise directions. To explore the role of neuromechanical dynamics, the instructed speeds covered a wide range: fast (near the limits of performance), medium (near preferred speed), and very slow (rendering dynamic effects negligible). Because kinematically constrained movements involve significant physical interaction, disentangling neural control from the influences of biomechanics presents a challenge. To address it, we modeled the interactive dynamics to "subtract off' peripheral biomechanics from observed force and kinematic data, thereby estimating aspects of underlying neural action that may be expressed in terms of motion. We demonstrate the value of this method: remarkably, an approximately elliptical path emerged. and speed minima coincided with curvature maxima, similar to what is seen in unconstrained movements, even though the hand moved at nearly constant speed along a constant-curvature path. These findings suggest that the neural controller takes advantage of peripheral biomechanics to simplify physical interaction. As a result, patterns seen in unconstrained movements persist even when physical interaction prevents their expression in hand kinematics. The reemergence of a speed-curvature relation indicates that it is due, at least in part, to neural processes that emphasize smoothness and predictability.NEW & NOTEWORTHY Physically interacting with kinematic constraints is commonplace in everyday actions. We report a study of humans turning a crank. a circular constraint that imposes constant hand path curvature and hence should suppress variations of hand speed due to the power-law speed-curvature relation widely reported for unconstrained motions. Remarkably, we found that, when peripheral biomechanical factors are removed, a speed-curvature relation reemerges, indicating that it is, at least in part, of neural origin.