Department of Biomedical and Neuromotor Sciences, University of Bologna, Piazza di Porta S. Donato 2, 40126, Bologna, Italy.
Laboratory of Neuro- and Psychophysiology, KU Leuven, 3000, Leuven, Belgium.
Brain Struct Funct. 2019 Sep;224(7):2537-2557. doi: 10.1007/s00429-019-01923-8. Epub 2019 Jul 20.
Area PE (Brodmann's area 5), located in the posterior parietal cortex (PPC), is involved in the control of arm movements. Many monkey studies showed PE's involvement in reach directions, while only a few revealed signals coding the depth of reaches. Notably, all these studies focused on the lateral part of PE, leaving its medial part functionally largely unexplored. We here recorded neuronal activity in the medial part of PE in three male Macaca fascicularis while they performed coordinated eye and arm movements in darkness towards targets located at different directions and depths. We used the same task as in our previous studies of more caudal PPC sectors (areas V6A and PEc), allowing a direct comparison between these three PPC areas. We found that, in medial PE, reach direction and depth were encoded mainly by distinct populations of neurons. Directional signals were more prominent before movement onset, whereas depth processing occurred mainly during and after movement execution. Visual and somatosensory mapping of medial PE revealed a lack of visual responses yet strong somatosensory sensitivity, with a representation of both upper and lower limbs, distinct from the somatotopy reported in lateral PE. This study shows that PE is strongly involved in motor processing of depth and direction information during reaching. It highlights a trend in medial PPC, going from the joint coding of depth and direction signals caudally, in area V6A, to a largely segregated processing of the two signals rostrally, in area PE.
位于顶后皮质（PPC）的运动前区（PE）在手臂运动的控制中发挥作用。许多猴子研究表明 PE 参与了到达方向的控制，而只有少数研究揭示了到达深度的信号编码。值得注意的是，所有这些研究都集中在 PE 的外侧部分，其内侧部分的功能在很大程度上仍未得到探索。我们在三只雄性恒河猴进行黑暗中协调的眼睛和手臂运动以到达位于不同方向和深度的目标时，记录了其 PPC 中部区域（PE 区和 V6A 区）的神经元活动。我们使用了与我们之前对更靠后的 PPC 区域（V6A 和 PEc 区）的研究相同的任务，使得这三个 PPC 区域之间可以进行直接比较。我们发现，在 PE 区的中部，到达方向和深度主要由不同的神经元群体编码。方向信号在运动开始前更为明显，而深度处理主要发生在运动执行期间和之后。对 PE 区的视觉和躯体感觉映射显示，其缺乏视觉反应，但具有很强的躯体感觉敏感性，对上肢和下肢均有代表，与外侧 PE 区报告的躯体感觉图式不同。这项研究表明，PE 在到达过程中深度和方向信息的运动处理中发挥了重要作用。它突出了一个趋势，即从中部的 V6A 区，深度和方向信号的联合编码，向更靠后的 PE 区，两个信号的高度分离处理发展。
