Descending motor drive and somatosensory feedback play important roles in modulating muscle activity. Numerous studies have characterized the organization of neuronal connectivity in which descending motor pathways and somatosensory afferents converge on spinal motor neurons as a final common pathway. However, how inputs from these two pathways are integrated into spinal motor neurons to generate muscle activity during actual motor behavior is unknown. Here, we simultaneously recorded activity in the motor cortices (MCx), somatosensory afferent neurons, and forelimb muscles in monkeys performing reaching and grasping movements. We constructed a linear model to explain the instantaneous muscle activity using the activity of MCx (descending input) and peripheral afferents (afferent input). Decomposition of the reconstructed muscle activity into each subcomponent indicated that muscle activity before movement onset could first be explained by descending input from mainly the primary motor cortex and muscle activity after movement onset by both descending and afferent inputs. Descending input had a facilitative effect on all muscles, whereas afferent input had a facilitative or suppressive effect on each muscle. Such antagonistic effects of afferent input can be explained by reciprocal effects of the spinal reflex. These results suggest that descending input contributes to the initiation of limb movement, and this initial movement subsequently affects muscle activity via the spinal reflex in conjunction with the continuous descending input. Thus, spinal motor neurons are subjected to temporally organized modulation by direct activation through the descending pathway and the lagged action of the spinal reflex during voluntary limb movement.

中文翻译：

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随意肢体运动的感觉运动会聚的时间动力学

下行电机驱动和体感反馈在调节肌肉活动中起着重要作用。许多研究已经表征了神经元连接的组织，其中下行运动通路和体感传入神经汇聚在脊髓运动神经元上作为最终的共同通路。然而，这两条通路的输入如何整合到脊髓运动神经元中以在实际运动行为期间产生肌肉活动尚不清楚。在这里，我们同时记录了运动皮层 (MCx)、体感传入神经元和猴子执行伸手和抓握动作的前肢肌肉的活动。我们构建了一个线性模型来使用 MCx（下行输入）和外周传入（传入输入）的活动来解释瞬时肌肉活动。将重建的肌肉活动分解为每个子成分表明，运动开始前的肌肉活动首先可以通过主要来自初级运动皮层的下行输入和运动开始后的肌肉活动通过下行和传入输入来解释。下行输入对所有肌肉都有促进作用，而传入输入对每块肌肉都有促进或抑制作用。传入输入的这种拮抗作用可以用脊髓反射的相互作用来解释。这些结果表明，下行输入有助于肢体运动的启动，并且这种初始运动随后通过脊髓反射结合连续下行输入影响肌肉活动。因此，