Department of Psychology, Vanderbilt University, Nashville, Tennessee.
J Comp Neurol. 2013 Nov;521(16):3768-90. doi: 10.1002/cne.23377.
The ventral posterior nucleus of thalamus sends highly segregated inputs into each digit representation in area 3b of primary somatosensory cortex. However, the spatial organization of the connections that link digit representations of areas 3b with other somatosensory areas is less understood. Here we examined the cortical inputs to individual digit representations of area 3b in four squirrel monkeys and one prosimian galago. Retrograde tracers were injected into neurophysiologically defined representations of individual digits of area 3b. Cortical tissues were cut parallel to the surface in some cases and showed that feedback projections to individual digits overlapped extensively in the hand representations of areas 3b, 1, and parietal ventral (PV) and second somatosensory (S2) areas. Other regions with overlapping populations of labeled cells included area 3a and primary motor cortex (M1). The results were confirmed in other cases in which the cortical tissues were cut in the coronal plane. The same cases also showed that cells were primarily labeled in the infragranular and supragranular layers. Thus, feedback projections to individual digit representations in area 3b mainly originate from multiple digits and other portions of hand representations of areas 3b, 1, PV, and S2. This organization is in stark contrast to the segregated thalamocortical inputs, which originate in single digit representations and terminate in the matching digit representation in the cortex. The organization of feedback connections could provide a substrate for the integration of information across the representations of adjacent digits in area 3b.
丘脑腹后核将高度分离的输入发送到初级体感皮层 3b 区的每个手指代表区。然而，将 3b 区的手指代表区与其他体感区连接的连接的空间组织尚不清楚。在这里，我们检查了四个松鼠猴和一个原猴灵长类动物的 3b 区单个手指代表区的皮质输入。逆行示踪剂被注射到神经生理学定义的单个手指的 3b 区代表区。在某些情况下，皮质组织与表面平行切割，并显示反馈投射到个体手指在 3b、1 和顶叶腹侧（PV）和第二体感（S2）区域的手部代表区中广泛重叠。其他具有重叠标记细胞群体的区域包括 3a 区和初级运动皮层（M1）。在其他情况下，通过冠状平面切割皮质组织来确认结果。同样的情况也表明细胞主要标记在颗粒下和颗粒上层。因此，3b 区单个手指代表区的反馈投射主要来自多个手指和 3b、1、PV 和 S2 区手部代表区的其他部分。这种组织与分离的丘脑皮质输入形成鲜明对比，后者起源于单个手指代表区，并在皮质中终止于匹配的手指代表区。反馈连接的组织可以为 3b 区相邻手指代表区的信息整合提供基础。
