What is the neural substrate that enables the cerebral cortex to control a single mystacial vibrissa and orchestrate its movement? To answer this question, we injected rabies virus into the intrinsic muscle that protracts the rat C3 vibrissa and used retrograde transneuronal transport to identify the cortical neurons that influence the muscle. A surprisingly diverse set of cortical areas is the origin of disynaptic control over the motoneurons that influence the C3 protractor. More than two thirds of these layer 5 pyramidal neurons (L5PNs) are dispersed in frontal and parietal areas outside the primary motor cortex (vM1). This observation emphasizes the importance of descending motor commands from non-primary motor areas. More than a third of the L5PNs originate from somatosensory areas, such as the barrel field (vS1). The barrel field has been long considered a prototypic model system for studying sensory processing at the level of the cerebral cortex. Even so, we find that the number of L5PNs in vS1, and even their peak density, rivals the number and peak density of L5PNs in vM1. Thus, our results emphasize the importance of the barrel field in processing motor output. The distribution of L5PNs in vM1 and vS1 leads us to propose a model of vibrissa protraction in which vM1 output results in protraction, and vS1 output results in reciprocal inhibition (suppression) of protraction. This paired initiation and suppression of complementary movements may be a general feature of the descending output from the rodent M1 and S1.

中文翻译：

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多个皮质系统影响单个触肌

使大脑皮层能够控制单个神秘的振动并协调其运动的神经基质是什么？为了回答这个问题，我们将狂犬病病毒注射到延长大鼠 C3 触肌的内在肌肉中，并使用逆行经神经元转运来识别影响肌肉的皮层神经元。一组令人惊讶的多样化皮质区域是对影响 C3 量角器的运动神经元的双坐控制的起源。这些第 5 层锥体神经元 （L5PN） 中超过三分之二分散在初级运动皮层 （vM1） 外的额叶和顶叶区域。这一观察强调了从非主要运动区域下降运动命令的重要性。超过三分之一的 L5PN 起源于体感区域，例如桶状场 （vS1）。长期以来，桶状视野一直被认为是研究大脑皮层水平感觉处理的原型模型系统。即便如此，我们发现 vS1 中 L5PN 的数量，甚至它们的峰值密度，都与 vM1 中 L5PN 的数量和峰值密度相当。因此，我们的结果强调了桶场在处理电机输出中的重要性。L5PNs 在 vM1 和 vS1 中的分布使我们提出了一个触观拉伸模型，其中 vM1 输出导致拉伸，而 vS1 输出导致拉伸的相互抑制（抑制）。这种互补运动的成对启动和抑制可能是啮齿动物 M1 和 S1 下降输出的一般特征。