BACKGROUND The function of the primate's posterior parietal cortex (PPC) in sensorimotor transformations is well-established, though in humans its complexity is still challenging. Well-established models indicate that the posterior parietal cortex influences motor output indirectly, by means of connections to the premotor cortex, which in turn is directly connected to the motor cortex. OBJECTIVE The possibility that the PPC could be at the origin of direct afferents to M1 has been suggested in humans but has never been confirmed directly. We aim to do so in the present study by using the novel technique of paired intraoperative cortical stimulation. METHODS In the present cross-sectional study, we assessed during intraoperative monitoring of the corticospinal tract in brain tumour patients the existence of short-latency effects of parietal stimulation on corticospinal excitability to the upper limb. MEPs were evoked by test stimuli over the motor cortex, which were preceded in some trials by conditioning stimuli on the PPC. RESULTS We identified two active cortical loci. One in the inferior parietal lobule exerted short-latency excitatory effects and one in the superior parietal lobule that drove short-latency inhibitory effects on cortical motor output. All active foci were distributed in the rostral portion of the PPC and on the postcentral sulcus. CONCLUSIONS For the first time in humans, the present data show direct evidence in favour of a distributed system of connections from the posterior parietal cortex to the ipsilateral primary motor cortex. In addition, we show that dual cortical stimulation is a novel and efficient technique to investigate intraoperative brain connectivity in the anaesthetized patient.

中文翻译：

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通过术中双皮质刺激评估的上顶叶和下顶叶小叶与运动皮层之间的皮质皮质连接

背景 灵长类动物的后顶叶皮层 (PPC) 在感觉运动转换中的功能已经确立，但在人类中其复杂性仍然具有挑战性。完善的模型表明后顶叶皮层通过与前运动皮层的连接间接影响运动输出，而前运动皮层又直接与运动皮层相连。目标 PPC 可能是 M1 直接传入的起源的可能性已在人类中提出，但从未直接得到证实。我们的目标是在本研究中通过使用配对术中皮层刺激的新技术来做到这一点。方法 在目前的横断面研究中，我们在脑肿瘤患者皮质脊髓束的术中监测期间评估了顶叶刺激对上肢皮质脊髓兴奋性的短潜伏期效应。MEP 是由运动皮层上的测试刺激引起的，在一些试验中，先于 PPC 上的条件刺激。结果我们确定了两个活跃的皮质位点。顶下小叶中的一个产生短潜伏期兴奋作用，顶上小叶中的一个产生对皮质运动输出的短潜伏期抑制作用。所有活动灶都分布在 PPC 的嘴部和中央后沟上。结论首次在人类中，目前的数据显示直接证据支持从后顶叶皮层到同侧初级运动皮层的分布式连接系统。此外，我们表明双皮质刺激是一种新颖且有效的技术，可用于研究麻醉患者的术中大脑连通性。