Flexible Cortical Control of Task-Specific Muscle Synergies
Flexible Cortical Control of Task-Specific Muscle Synergies
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DOI：
10.1523/jneurosci.5481-11.2012
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发表时间：
2012-09-05
影响因子：
5.3
通讯作者：
Jackson, Andrew
中科院分区：
文献类型：
--
作者：
Nazarpour, Kianoush;Barnard, Amy;Jackson, Andrew
运动中肌肉活动的关联结构通常被解释为对上肢功能的低水平、硬连接限制的证据。然而，肌肉协同效应也可能出现在最优策略中，以在冗余的控制空间内实现高水平的任务目标。为了区分这些不同的解释，我们检查了肌电接口操作过程中肌肉变异性的结构，在该接口中，任务限制与自然肢体生物力学分离。我们发现，通过练习，人类受试者学会了在任意一对手和前臂肌肉之间形成适当的协变模式，以适合于在逐一试验的基础上改变方向的椭圆形目标。因此，尽管在效应器空间中达到了相同的平均位置，但通过将可变性缓冲到那些对任务成功影响最小的维度中，性能得到了改善。对β频率肌肉间连贯性的任务调制表明，不同皮质脊髓通路的不同招募有助于肌肉之间的正相关。然而，这种前馈机制不能解释在视觉反馈存在时观察到的负相关性。第二个实验揭示了快速的、依赖于目标的视觉反应的发展，这与纠正主要与任务相关的错误的“最小干预”控制相一致。这些机制共同促进了适合于广泛抽象任务目标的任务特定肌肉协同效应的动态出现。
Correlation structure in the activity of muscles across movements is often interpreted as evidence for low-level, hardwired constraints on upper-limb function. However, muscle synergies may also emerge from optimal strategies to achieve high-level task goals within a redundant control space. To distinguish these contrasting interpretations, we examined the structure of muscle variability during operation of a myoelectric interface in which task constraints were dissociated from natural limb biomechanics. We found that, with practice, human subjects learned to shape patterns of covariation between arbitrary pairs of hand and forearm muscles appropriately for elliptical targets whose orientation varied on a trial-by-trial basis. Thus, despite arriving at the same average location in the effector space, performance was improved by buffering variability into those dimensions that least impacted task success. Task modulation of beta-frequency intermuscular coherence indicated that differential recruitment of divergent corticospinal pathways contributed to positive correlations among muscles. However, this feedforward mechanism could not account for negative correlations observed in the presence of visual feedback. A second experiment revealed the development of fast, target-dependent visual responses consistent with "minimum intervention" control correcting predominantly task-relevant errors. Together, these mechanisms contribute to the dynamic emergence of task-specific muscle synergies appropriate for a wide range of abstract task goals.