Department of Kinesiology, The Pennsylvania State University , University Park, Pennsylvania.
J Neurophysiol. 2018 Sep 1;120(3):1045-1060. doi: 10.1152/jn.00045.2018. Epub 2018 Jun 6.
We combined the theory of neural control of movement with referent coordinates and the uncontrolled manifold hypothesis to investigate multifinger coordination. We tested hypotheses related to stabilization of performance by covarying control variables, translated into apparent stiffness and referent coordinate, at different levels of an assumed hierarchy of control. Subjects produced an accurate combination of total force and total moment of force with the four fingers under visual feedback on both variables and after feedback was partly or completely removed. The "inverse piano" device was used to estimate control variables. We observed strong synergies in the space of hypothetical control variables that stabilized total force and moment of force, as well as weaker synergies stabilizing individual finger forces; whereas the former were attenuated by alteration of visual feedback, the latter were much less affected. In addition, we investigated the organization of "ascending synergies" stabilizing task-level control variables by covaried adjustments of finger-level control variables. We observed intertrial covariation of individual fingers' referent coordinates that stabilized hand-level referent coordinate, but we observed no such covariation for apparent stiffness. The observations suggest the existence of both descending and ascending synergies in a hierarchical control system. They confirm a trade-off between synergies at different levels of control and corroborate the hypothesis on specialization of different fingers for the control of force and moment. The results provide strong evidence for the importance of central back-coupling loops in ensuring stability of action. NEW & NOTEWORTHY We expand analysis of action in the space of hypothetical control variables to hierarchically organized multieffector systems. We also introduce the novel concept of ascending synergies, which reflect covariation of control variables to individual effectors (fingers) that stabilize task-specific control variables at a hierarchically higher, task-specific level (hand).
我们将运动的神经控制理论与参照坐标和未受控制的流形假设相结合，研究多指协调。我们测试了与通过协变控制变量（转化为明显的刚度和参照坐标）在假设的控制层次的不同水平上稳定性能相关的假设。在视觉反馈下，受试者使用“逆钢琴”设备来估计控制变量，以产生总力和总力矩与四个手指的准确组合，反馈部分或完全移除后也是如此。我们观察到在稳定总力和力矩的假设控制变量空间中存在很强的协同作用，以及在稳定单个手指力的较弱协同作用；前者随着视觉反馈的改变而减弱，后者则受影响较小。此外，我们通过手指水平控制变量的协变调整来研究稳定任务水平控制变量的“上行协同作用”的组织。我们观察到手水平参照坐标的稳定手水平参照坐标的单个手指参照坐标的试验间协变，但我们没有观察到明显刚度的这种协变。观察结果表明，在分层控制系统中存在下行和上行协同作用。它们证实了不同控制水平的协同作用之间存在权衡，并证实了不同手指专门用于力和力矩控制的假设。结果为中央后反馈回路在确保动作稳定性方面的重要性提供了有力证据。新增及值得注意之处：我们将在假设控制变量空间中的动作分析扩展到分层组织的多效器系统。我们还引入了上行协同作用的新概念，它反映了控制变量到个体效应器（手指）的协变，这些效应器稳定了分层更高、特定任务的控制变量（手）。
