Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, Alberta, Canada.
J Neurophysiol. 2021 Feb 1;125(2):628-637. doi: 10.1152/jn.00531.2020. Epub 2021 Jan 20.
The mammalian motor cortex is topographically organized into representations of discrete body parts (motor maps). Studies in adult rats using long-duration intracortical microstimulation (LD-ICMS) reveal that forelimb motor cortex is functionally organized into several spatially distinct areas encoding complex, multijoint movement sequences: elevate, advance, grasp, and retract. The topographical arrangement of complex movements during development and the influence of skilled learning are unknown. Here, we determined the emergence and topography of complex forelimb movement representations in rats between () and . We further investigated the expression of the maps for complex movements under conditions of reduced cortical inhibition and whether skilled forelimb motor training could alter their developing topography. We report that simple forelimb movements are first evoked at and are confined to the caudal forelimb area (CFA), whereas complex movements first reliably appear at and are observed in both the caudal and rostral forelimb areas (RFA). During development, the topography of complex movement representations undergoes reorganization with "grasp" and "elevate" movements predominantly observed in the RFA and all four complex movements observed in CFA. Under reduced cortical inhibition, simple and complex movements were first observed in the CFA on and , respectively, and the topography is altered relative to a saline control. Further, skilled motor learning was associated with increases in "grasp" and "retract" representations specific to the trained limb. Our results demonstrate that early-life motor experience during development can modify the topography of complex forelimb movement representations. The motor cortex is topographically organized into maps of different body parts. We used to think that the function of motor cortex was to drive individual muscles, but more recently we have learned that it is also organized to make complex movements. However, the development and plasticity of those complex movements is completely unknown. In this paper, the emergence and topography of complex movement representation, as well as their plasticity during development, is detailed.
哺乳动物的运动皮层在身体部位上具有拓扑组织（运动图）。在成年大鼠中进行的长时间皮层内微刺激（LD-ICMS）研究表明，前肢运动皮层在功能上被组织成几个空间上不同的区域，用于编码复杂的多关节运动序列：抬高、前进、抓握和缩回。在发育过程中复杂运动的拓扑排列和熟练学习的影响是未知的。在这里，我们确定了大鼠（）至（）之间复杂前肢运动代表的出现和拓扑结构。我们进一步研究了在皮质抑制减少的情况下复杂运动图的表达，以及熟练的前肢运动训练是否可以改变其发育的拓扑结构。我们报告说，简单的前肢运动首先在出现，并且仅限于前肢尾部区域（CFA），而复杂的运动首先可靠地在出现，并且在 CFA 和前肢头部区域（RFA）中观察到。在发育过程中，复杂运动代表的拓扑结构经历了重新组织，“抓握”和“抬高”运动主要出现在 RFA 中，而所有四个复杂运动都出现在 CFA 中。在皮质抑制减少的情况下，简单和复杂运动分别在和首次出现在 CFA 中，并且相对于盐水对照，拓扑结构发生了改变。此外，熟练的运动学习与训练肢体特有的“抓握”和“缩回”代表的增加有关。我们的结果表明，发育过程中的早期运动经验可以改变复杂前肢运动代表的拓扑结构。运动皮层在身体不同部位的地图上进行组织。我们过去认为运动皮层的功能是驱动单个肌肉，但最近我们了解到它也被组织起来以进行复杂的运动。然而，这些复杂运动的发展和可塑性是完全未知的。在本文中，详细描述了复杂运动代表的出现和拓扑结构，以及它们在发育过程中的可塑性。
