Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada.
J Neurophysiol. 2010 Jan;103(1):564-72. doi: 10.1152/jn.00791.2009. Epub 2009 Nov 18.
Correlations between neural activity in primary motor cortex (M1) and arm kinematics have recently been shown to be temporally extensive and spatially complex. These results provide a sophisticated account of M1 processing and suggest that M1 neurons encode high-level movement trajectories, termed "pathlets." However, interpreting pathlets is difficult because the mapping between M1 activity and arm kinematics is indirect: M1 activity can generate movement only via spinal circuitry and the substantial complexities of the musculoskeletal system. We hypothesized that filter-like complexities of the musculoskeletal system are sufficient to generate temporally extensive and spatially complex correlations between motor commands and arm kinematics. To test this hypothesis, we extended the computational and experimental method proposed for extracting pathlets from M1 activity to extract pathlets from muscle activity. Unlike M1 activity, it is clear that muscle activity does not encode arm kinematics. Accordingly, any spatiotemporal correlations in muscle pathlets can be attributed to musculoskeletal complexities rather than explicit higher-order representations. Our results demonstrate that extracting muscle pathlets is a robust and repeatable process. Pathlets extracted from the same muscle but different subjects or from the same muscle on different days were remarkably similar and roughly appropriate for that muscle's mechanical action. Critically, muscle pathlets included extensive spatiotemporal complexity, including kinematic features before and after the present muscle activity, similar to that reported for M1 neurons. These results suggest the possibility that M1 pathlets at least partly reflect the filter-like complexities of the periphery rather than high-level representations.
最近的研究表明，初级运动皮层（M1）中的神经活动与手臂运动学之间的相关性在时间上广泛存在，在空间上也很复杂。这些结果提供了对 M1 处理的复杂描述，并表明 M1 神经元编码了高级运动轨迹，称为“路径片段”。然而，解释路径片段是困难的，因为 M1 活动与手臂运动学之间的映射是间接的：M1 活动只能通过脊髓电路和肌肉骨骼系统的大量复杂结构来产生运动。我们假设肌肉骨骼系统的滤波器样复杂性足以产生运动指令和手臂运动学之间的时间上广泛和空间上复杂的相关性。为了验证这一假设，我们将从 M1 活动中提取路径片段的计算和实验方法扩展到从肌肉活动中提取路径片段。与 M1 活动不同，很明显，肌肉活动并不编码手臂运动学。因此，肌肉路径片段中的任何时空相关性都可以归因于肌肉骨骼复杂性，而不是明确的更高阶表示。我们的研究结果表明，提取肌肉路径片段是一个稳健且可重复的过程。从同一肌肉但不同个体或同一肌肉在不同天提取的路径片段非常相似，大致适合该肌肉的机械动作。关键是，肌肉路径片段包括广泛的时空复杂性，包括当前肌肉活动前后的运动学特征，与报告的 M1 神经元相似。这些结果表明，M1 路径片段至少部分反映了外围的滤波器样复杂性，而不是高级表示。
