Neuroscience Program, Emory University, Atlanta, Georgia 30332-0535, USA.
J Neurophysiol. 2013 Jan;109(1):31-45. doi: 10.1152/jn.00684.2012. Epub 2012 Oct 24.
We hypothesized that motor outputs are hierarchically organized such that descending temporal commands based on desired task-level goals flexibly recruit muscle synergies that specify the spatial patterns of muscle coordination that allow the task to be achieved. According to this hypothesis, it should be possible to predict the patterns of muscle synergy recruitment based on task-level goals. We demonstrated that the temporal recruitment of muscle synergies during standing balance control was robustly predicted across multiple perturbation directions based on delayed sensorimotor feedback of center of mass (CoM) kinematics (displacement, velocity, and acceleration). The modulation of a muscle synergy's recruitment amplitude across perturbation directions was predicted by the projection of CoM kinematic variables along the preferred tuning direction(s), generating cosine tuning functions. Moreover, these findings were robust in biphasic perturbations that initially imposed a perturbation in the sagittal plane and then, before sagittal balance was recovered, perturbed the body in multiple directions. Therefore, biphasic perturbations caused the initial state of the CoM to differ from the desired state, and muscle synergy recruitment was predicted based on the error between the actual and desired upright state of the CoM. These results demonstrate that that temporal motor commands to muscle synergies reflect task-relevant error as opposed to sensory inflow. The proposed hierarchical framework may represent a common principle of motor control across motor tasks and levels of the nervous system, allowing motor intentions to be transformed into motor actions.
我们假设运动输出是分层组织的，使得基于期望任务级目标的下降时间命令灵活地招募肌肉协同作用，指定肌肉协调的空间模式，从而实现任务。根据这一假设，应该有可能根据任务级目标预测肌肉协同作用的招募模式。我们证明，在基于中心质量 (CoM) 运动学（位移、速度和加速度的延迟感觉运动反馈）的多个扰动方向上，站立平衡控制期间肌肉协同作用的时间招募是稳健可预测的。肌肉协同作用在扰动方向上的募集幅度的调制是由 CoM 运动学变量沿着优选调谐方向（s）的投影预测的，产生余弦调谐函数。此外，这些发现对于双相扰动是稳健的，双相扰动最初在矢状面施加扰动，然后在恢复矢状平衡之前，以多种方向扰动身体。因此，双相扰动导致 CoM 的初始状态与期望状态不同，并且根据 CoM 的实际和期望直立状态之间的误差来预测肌肉协同作用的招募。这些结果表明，肌肉协同作用的时间运动命令反映了与任务相关的误差，而不是感觉输入。所提出的分层框架可能代表了运动任务和神经系统各级的运动控制的共同原则，允许运动意图转化为运动动作。
