Goldman-Rakic P S, Porrino L J
J Comp Neurol. 1985 Dec 22;242(4):535-60. doi: 10.1002/cne.902420406.
The frontal lobe projections of the mediodorsal (MD) nucleus of the thalamus were examined in rhesus monkey by transport of retrograde markers injected into one of nine cytoarchitectonic regions (Walker's areas 6, 8A, 9, 10, 11, 12, 13, 46, and Brodmann's area 4) located in the rostral third of the cerebrum. Each area of prefrontal, premotor, or motor cortex injected was found to receive a topographically unique thalamic input from clusters of cells in specific subdivisions within MD. All of the prefrontal areas examined also receive topographically organized inputs from other thalamic nuclei including, most prominently, the ventral anterior (VA) and medial pulvinar nuclei. Conversely, and in agreement with previous findings, MD projects to areas of the frontal lobe beyond the traditional borders of prefrontal cortex, such as the anterior cingulate and supplementary motor cortex. The topography of thalamocortical neurons revealed in coronal sections through VA, MD, and pulvinar is circumferential. In the medial part of MD, for example, thalamocortical neurons shift from a dorsal to a ventral position for cortical targets lying medial to lateral along the ventral surface of the lobe; neurons in the lateral MD move from a ventral to a dorsal position, for cortical areas situated lateral to medial on the convexity of the hemisphere. The aggregate evidence for topographic specificity is supported further by experiments in which different fluorescent dyes were placed in multiple areas of the frontal lobe in each of three cases. The results show that very few, if any, thalamic neurons project to more than one area of cortex. The widespread cortical targets of MD neurons together with evidence for multiple thalamic inputs to prefrontal areas support a revision of the classical hodological definition of prefrontal cortex as the exclusive cortical recipient of MD projections. Rather, the prefrontal cortex is defined by multiple specific relationships with the thalamus.
通过将逆行标记物注入位于大脑前三分之一的九个细胞构筑区域（沃克氏区6、8A、9、10、11、12、13、46和布罗德曼区4）之一，研究了恒河猴丘脑内侧背核（MD）的额叶投射。发现注入的前额叶、运动前区或运动皮层的每个区域都从MD内特定亚区的细胞簇接收地形上独特的丘脑输入。所有检查的前额叶区域还从其他丘脑核接收地形组织化的输入，其中最突出的是腹前核（VA）和内侧丘脑枕核。相反，与先前的发现一致，MD投射到前额叶皮层传统边界之外的额叶区域，如前扣带回和辅助运动皮层。通过VA、MD和丘脑枕的冠状切片显示的丘脑皮质神经元的地形是圆周性的。例如，在MD的内侧部分，丘脑皮质神经元沿着叶腹表面从背侧到腹侧移位，以对应位于内侧到外侧的皮质靶点；外侧MD中的神经元则从腹侧到背侧移位，以对应位于半球凸面上从外侧到内侧的皮质区域。在三个案例中的每一个案例中，将不同的荧光染料放置在额叶的多个区域的实验进一步支持了地形特异性的总体证据。结果表明，极少有丘脑神经元（如果有的话）投射到一个以上的皮质区域。MD神经元广泛的皮质靶点以及前额叶区域有多个丘脑输入的证据支持了对前额叶皮层经典传导路定义的修订，即前额叶皮层是MD投射的唯一皮质接受者。相反，前额叶皮层是由与丘脑的多种特定关系定义的。
