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, multi-joint movement sequences: elevate, advance, grasp, retract. The topographical arrangement of complex movements during development and the influence of skilled learning is unknown. Here we determined the emergence and topography of complex forelimb movement representations in rats between postnatal days (PND) 13 to 60. 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 PND 25 and are confined to the caudal forelimb area (CFA), whereas complex movements first reliably appear at PND 30 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 PND 15 and 20 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.

中文翻译：

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复杂运动表示的发展和可塑性。

哺乳动物运动皮层在地形上被组织成离散身体部位的表示（运动图）。使用长时间皮层内微刺激 (LD-ICMS) 对成年大鼠的研究表明，前肢运动皮层在功能上被组织成几个空间不同的区域，编码复杂的多关节运动序列：抬高、前进、抓握、缩回。发育过程中复杂运动的地形排列和熟练学习的影响是未知的。在这里，我们确定了出生后第 13 天到第 60 天之间大鼠复杂前肢运动表征的出现和地形。我们进一步研究了在皮质抑制减少的情况下复杂运动图谱的表达，以及熟练的前肢运动训练是否可以改变他们的发展地形。我们报告说，简单的前肢运动首先在 PND 25 时引起，并且仅限于尾前肢区域 (CFA)，而复杂的运动首先可靠地出现在 PND 30 并在尾侧和前肢前肢区域 (RFA) 中观察到。在开发过程中，复杂运动表征的地形经过重组，主要在 RFA 中观察到的“抓握”和“提升”运动以及在 CFA 中观察到的所有四种复杂运动。在皮质抑制减少的情况下，首先分别在 PND 15 和 20 的 CFA 中观察到简单和复杂的运动，并且相对于盐水对照，地形发生了改变。此外，熟练的运动学习与训练肢体特有的“抓握”和“收回”表征的增加有关。