Yabuta N H, Callaway E M
Systems Neurobiology Laboratories, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
J Neurosci. 1998 Nov 15;18(22):9489-99. doi: 10.1523/JNEUROSCI.18-22-09489.1998.
The primate visual system is composed of multiple, functionally specialized cortical areas. The functional diversity among areas is thought to reflect different contributions from early parallel visual pathways to the area V1 neurons providing input to "higher" cortical areas. The M pathway is believed to provide information about motion and contrast, via layer 4B of V1, to dorsal visual areas. The P pathway is believed to provide information about shape and color, via layer 2/3 of V1, to ventral visual areas, with specialized contributions from cytochrome-oxidase (CO) blob versus interblob neurons. However, the detailed anatomical relationships between the M and P pathways and the neurons in V1 that provide input to higher extrastriate cortical areas are poorly understood. To study these relationships, spiny stellate neurons in the M- and P-recipient layers of V1, 4Calpha and 4Cbeta, respectively, were intracellularly labeled, and their axonal and dendritic arbors were reconstructed. We find that neurons with dendrites in upper layer 4Calpha project axons to layer 4B and CO blobs in layer 2/3, thus relaying M input to these regions. Other neurons in lower layer 4Calpha provide M input to interblobs. These cells have either (1) dendrites restricted to lower layer 4Calpha and axons specifically targeting layer 2/3 interblobs, or (2) dendrites in lower 4Calpha and 4Cbeta and axons targeting blobs and interblobs. P-recipient layer 4Cbeta neurons have dense axonal arbors in both blobs and interblobs but not layer 4B. Quantitative analyses reveal that 4Calpha cells provide approximately five times more synapses than 4Cbeta cells to layer 4B, whereas 4Cbeta cells provide five times more synapses than 4Calpha cells to layer 2/3. These observations imply that M input is dominant in layer 4B. In layer 2/3, both blobs and interblobs receive M and P input, but the P input is dominant, and M input to interblobs derives exclusively from a subpopulation of M afferents that targets lower 4Calpha, not from afferents targeting only upper 4Calpha (cf. Blasdel and Lund, 1983). We speculate that the M and P pathways to interblobs are "X-like" linear systems, whereas blobs also receive nonlinear "Y-like" M input.
灵长类动物的视觉系统由多个功能专门化的皮质区域组成。这些区域之间的功能多样性被认为反映了早期平行视觉通路对向“更高”皮质区域提供输入的V1神经元的不同贡献。M通路被认为通过V1的4B层向背侧视觉区域提供有关运动和对比度的信息。P通路被认为通过V1的2/3层向腹侧视觉区域提供有关形状和颜色的信息，细胞色素氧化酶（CO）斑点神经元和斑点间神经元有专门的贡献。然而，M和P通路与向更高的纹外皮质区域提供输入的V1神经元之间的详细解剖关系却知之甚少。为了研究这些关系，分别在V1的M和P接收层（4Cα和4Cβ）中的棘状星状神经元进行了细胞内标记，并重建了它们的轴突和树突分支。我们发现，在4Cα上层有树突的神经元将轴突投射到4B层和2/3层的CO斑点，从而将M输入传递到这些区域。4Cα下层的其他神经元向斑点间提供M输入。这些细胞要么（1）树突局限于4Cα下层，轴突专门靶向2/3层的斑点间，要么（2）树突在4Cα和4Cβ下层，轴突靶向斑点和斑点间。P接收层4Cβ神经元在斑点和斑点间都有密集的轴突分支，但在4B层没有。定量分析表明，4Cα细胞向4B层提供的突触比4Cβ细胞多约五倍，而4Cβ细胞向2/3层提供的突触比4Cα细胞多五倍。这些观察结果表明M输入在4B层占主导地位。在2/3层，斑点和斑点间都接收M和P输入，但P输入占主导地位，向斑点间的M输入仅来自靶向4Cα下层的M传入神经元亚群，而不是仅靶向4Cα上层的传入神经元（参见Blasdel和Lund，1983）。我们推测，向斑点间的M和P通路是“X样”线性系统，而斑点也接收非线性 “Y样” M输入。
