Richard Nathalie, Desmurget Michel, Teillac Achille, Beuriat Pierre-Aurélien, Bardi Lara, Coudé Gino, Szathmari Alexandru, Mottolese Carmine, Sirigu Angela, Hiba Bassem
Institute of Cognitive Neuroscience Marc Jeannerod, CNRS / UMR 5229, 69500 Bron, France; Université Claude Bernard, Lyon 1, 69100 Villeurbanne, France.
Institute of Cognitive Neuroscience Marc Jeannerod, CNRS / UMR 5229, 69500 Bron, France; Université Claude Bernard, Lyon 1, 69100 Villeurbanne, France; Institut de neurosciences cognitives et intégratives d'Aquitaine, CNRS / UMR 5287, 33076 Bordeaux, France.
Neuroimage. 2021 Jul 15;235:118002. doi: 10.1016/j.neuroimage.2021.118002. Epub 2021 Mar 28.
The dorso-posterior parietal cortex (DPPC) is a major node of the grasp/manipulation control network. It is assumed to act as an optimal forward estimator that continuously integrates efferent outflows and afferent inflows to modulate the ongoing motor command. In agreement with this view, a recent per-operative study, in humans, identified functional sites within DPPC that: (i) instantly disrupt hand movements when electrically stimulated; (ii) receive short-latency somatosensory afferences from intrinsic hand muscles. Based on these results, it was speculated that DPPC is part of a rapid grasp control loop that receives direct inputs from the hand-territory of the primary somatosensory cortex (S1) and sends direct projections to the hand-territory of the primary motor cortex (M1). However, evidence supporting this hypothesis is weak and partial. To date, projections from DPPC to M1 grasp zone have been identified in monkeys and have been postulated to exist in humans based on clinical and transcranial magnetic studies. This work uses diffusion-MRI tractography in two samples of right- (n = 50) and left-handed (n = 25) subjects randomly selected from the Human Connectome Project. It aims to determine whether direct connections exist between DPPC and the hand control sectors of the primary sensorimotor regions. The parietal region of interest, related to hand control (hereafter designated DPPC), was defined permissively as the 95% confidence area of the parietal sites that were found to disrupt hand movements in the previously evoked per-operative study. In both hemispheres, irrespective of handedness, we found dense ipsilateral connections between a restricted part of DPPC and focal sectors within the pre and postcentral gyrus. These sectors, corresponding to the hand territories of M1 and S1, targeted the same parietal zone (spatial overlap > 92%). As a sensitivity control, we searched for potential connections between the angular gyrus (AG) and the pre and postcentral regions. No robust pathways were found. Streamline densities identified using AG as the starting seed represented less than 5 % of the streamline densities identified from DPPC. Together, these results support the existence of a direct sensory-parietal-motor loop suited for fast manual control and more generally, for any task requiring rapid integration of distal sensorimotor signals.
背侧后顶叶皮层（DPPC）是抓握/操作控制网络的一个主要节点。它被认为是一个最佳的前向估计器，不断整合传出信号和传入信号，以调节正在进行的运动指令。与这一观点一致的是，最近一项针对人类的术中研究确定了DPPC内的功能位点：（i）电刺激时会立即干扰手部运动；（ii）接收来自手部固有肌肉的短潜伏期体感传入信号。基于这些结果，有人推测DPPC是快速抓握控制回路的一部分，该回路接收来自初级体感皮层（S1）手部区域的直接输入，并向初级运动皮层（M1）手部区域发送直接投射。然而，支持这一假设的证据薄弱且不完整。迄今为止，已在猴子身上确定了从DPPC到M1抓握区的投射，并根据临床和经颅磁研究推测人类也存在这种投射。这项研究使用扩散磁共振成像纤维束成像技术，对从人类连接体项目中随机选取的两组样本进行研究，一组是右利手（n = 50），另一组是左利手（n = 25）。其目的是确定DPPC与初级感觉运动区域的手部控制区之间是否存在直接连接。与手部控制相关的顶叶感兴趣区域（以下称为DPPC）被宽松地定义为在先前的术中研究中发现会干扰手部运动的顶叶位点的95%置信区域。在两个半球中，无论利手情况如何，我们都发现DPPC的一个受限部分与中央前回和中央后回内的局部区域之间存在密集的同侧连接。这些区域对应于M1和S1的手部区域，靶向相同的顶叶区域（空间重叠> 92%）。作为敏感性对照，我们搜索了角回（AG）与中央前回和中央后回区域之间的潜在连接。未发现强大的通路。以AG为起始种子确定的纤维束密度不到从DPPC确定的纤维束密度的5%。总之，这些结果支持存在一个直接的感觉-顶叶-运动回路，适用于快速手动控制，更普遍地说，适用于任何需要快速整合远端感觉运动信号的任务。
