In the macaque brain, projections from distant, interconnected cortical areas converge in specific zones of the striatum. For example, specific zones of the motor putamen are targets of projections from frontal motor, inferior parietal, and ventrolateral prefrontal hand-related areas and thus are integral part of the so-called "lateral grasping network." In the present study, we analyzed the laminar distribution of corticostriatal neurons projecting to different parts of the motor putamen. Retrograde neural tracers were injected in different parts of the putamen in 3 Macaca mulatta (one male) and the laminar distribution of the labeled corticostriatal neurons was analyzed quantitatively. In frontal motor areas and frontal operculum, where most labeled cells were located, almost everywhere the proportion of corticostriatal labeled neurons in layers III and/or VI was comparable or even stronger than in layer V. Furthermore, within these regions, the laminar distribution pattern of corticostriatal labeled neurons largely varied independently from their density and from the projecting area/sector, but likely according to the target striatal zone. Accordingly, the present data show that cortical areas may project in different ways to different striatal zones, which can be targets of specific combinations of signals originating from the various cortical layers of the areas of a given network. These observations extend current models of corticostriatal interactions, suggesting more complex modes of information processing in the basal ganglia for different motor and nonmotor functions and opening new questions on the architecture of the corticostriatal circuitry.

SIGNIFICANCE STATEMENT Projections from the ipsilateral cerebral cortex are the major source of input to the striatum. Previous studies have provided evidence for distinct zones of the putamen specified by converging projections from specific sets of interconnected cortical areas. The present study shows that the distribution of corticostriatal neurons in the various layers of the primary motor and premotor areas varies depending on the target striatal zone. Accordingly, different striatal zones collect specific combinations of signals from the various cortical layers of their input areas, possibly differing in terms of coding, timing, and direction of information flow (e.g., feed-forward, or feed-back).

在猕猴大脑中，来自遥远、相互连接的皮层区域的投影会聚在纹状体的特定区域。例如，运动壳核的特定区域是额叶运动、下顶叶和腹外侧前额叶手相关区域的投射目标，因此是所谓的“横向抓握网络”的组成部分。在本研究中，我们分析了投射到运动壳核不同部位的皮质纹状体神经元的层流分布。逆行神经示踪剂注射到3只猕猴壳核的不同部位（一名男性）和标记的皮质纹状体神经元的层流分布进行了定量分析。在大多数标记细胞所在的额叶运动区和额叶盖中，几乎所有地方，III 和/或 VI 层中皮质纹状体标记神经元的比例与 V 层相当甚至更强。 此外，在这些区域内，层流分布模式皮质纹状体标记神经元的数量在很大程度上独立于它们的密度和投影区域/扇区而变化，但可能根据目标纹状体区域而变化。因此，目前的数据表明，皮层区域可能以不同的方式投射到不同的纹状体区域，这些区域可以成为源自给定网络区域的各个皮层层的特定信号组合的目标。

重要性声明来自同侧大脑皮层的投射是纹状体输入的主要来源。先前的研究已经为特定的相互连接的皮层区域的特定集合的投影所指定的壳核的不同区域提供了证据。本研究表明，皮质纹状体神经元在初级运动区和运动前区的各个层中的分布因目标纹状体区而异。因此，不同的纹状体区从其输入区域的各个皮层层收集信号的特定组合，可能在编码、时间和信息流方向（例如，前馈或反馈）方面有所不同。