Corticospinal neurons (CSNs) represent the direct cortical outputs to the spinal cord and play important roles in motor control across different species. However, their organizational principle remains unclear. By using a retrograde labeling system, we defined the requirement of CSNs in the execution of a skilled forelimb food-pellet retrieval task in mice. In vivo imaging of CSN activity during performance revealed the sequential activation of topographically ordered functional ensembles with moderate local mixing. Region-specific manipulations indicate that CSNs from caudal or rostral forelimb area control reaching or grasping, respectively, and both are required in the transitional pronation step. These region-specific CSNs terminate in different spinal levels and locations, therefore preferentially connecting with the premotor neurons of muscles engaged in different steps of the task. Together, our findings suggest that spatially defined groups of CSNs encode different movement modules, providing a logic for parallel-ordered corticospinal circuits to orchestrate multistep motor skills.

中文翻译：

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解构皮质脊髓回路以实现目标定向的运动技能。

皮质脊髓神经元（CSN）代表直接向脊髓的皮质输出，并在跨不同物种的运动控制中发挥重要作用。但是，它们的组织原则仍然不清楚。通过使用逆行标记系统，我们定义了在小鼠中执行熟练的前肢食物颗粒检索任务中CSN的要求。在表演过程中CSN活性的体内成像显示，在适度的局部混合下，顺序激活了地形有序的功能集合。特定于区域的操作表明，来自尾或前额前肢区域控制的CSN分别达到或抓握，并且在过渡旋前步骤中都需要这两个CSN。这些特定于区域的CSN在不同的脊柱水平和位置终止，因此，优先与参与任务不同步骤的肌肉的运动前神经元连接。总之，我们的发现表明，空间定义的CSN组编码不同的运动模块，为并行排列的皮质脊髓回路提供逻辑，以协调多步运动技能。