Yarch Jeff, Federer Frederick, Angelucci Alessandra
Department of Ophthalmology and Visual Science, Moran Eye Institute, University of Utah, Salt Lake City, Utah 84132.
Department of Ophthalmology and Visual Science, Moran Eye Institute, University of Utah, Salt Lake City, Utah 84132
J Neurosci. 2017 Jan 11;37(2):422-436. doi: 10.1523/JNEUROSCI.2848-16.2016.
Decades of anatomical studies on the primate primary visual cortex (V1) have led to a detailed diagram of V1 intrinsic circuitry, but this diagram lacks information about the output targets of V1 cells. Understanding how V1 local processing relates to downstream processing requires identification of neuronal populations defined by their output targets. In primates, V1 layers (L)2/3 and 4B send segregated projections to distinct cytochrome oxidase (CO) stripes in area V2: neurons in CO blob columns project to thin stripes while neurons outside blob columns project to thick and pale stripes, suggesting functional specialization of V1-to-V2 CO streams. However, the conventional diagram of V1 shows all L4B neurons, regardless of their soma location in blob or interblob columns, as projecting selectively to CO blobs in L2/3, suggesting convergence of blob/interblob information in L2/3 blobs and, possibly, some V2 stripes. However, it is unclear whether all L4B projection neurons show similar local circuitries. Using viral-mediated circuit tracing, we have identified the local circuits of L4B neurons projecting to V2 thick stripes in macaque. Consistent with previous studies, we found the somata of this L4B subpopulation to reside predominantly outside blob columns; however, unlike previous descriptions of local L4B circuits, these cells consistently projected outside CO blob columns in all layers. Thus, the local circuits of these L4B output neurons, just like their extrinsic projections to V2, preserve CO streams. Moreover, the intra-V1 laminar patterns of axonal projections identify two distinct neuron classes within this L4B subpopulation, including a rare novel neuron type, suggestive of two functionally specialized output channels.
Conventional diagrams of primate primary visual cortex (V1) depict neuronal connections within and between different V1 layers, but lack information about the cells' downstream targets. This information is critical to understanding how local processing in V1 relates to downstream processing. We have identified the local circuits of a population of cells in V1 layer (L)4B that project to area V2. These cells' local circuits differ from classical descriptions of L4B circuits in both the laminar and functional compartments targeted by their axons, and identify two neuron classes. Our results demonstrate that both local intra-V1 and extrinsic V1-to-V2 connections of L4B neurons preserve CO-stream segregation, suggesting that across-stream integration occurs downstream of V1, and that output targets dictate local V1 circuitry.
数十年来对灵长类动物初级视觉皮层（V1）的解剖学研究已得出V1内在神经回路的详细图谱，但该图谱缺乏有关V1细胞输出靶点的信息。要了解V1局部处理如何与下游处理相关联，需要识别由其输出靶点定义的神经元群体。在灵长类动物中，V1的第2/3层（L2/3）和第4B层向V2区不同的细胞色素氧化酶（CO）条带发送分离的投射：CO斑块柱中的神经元投射到细条带，而斑块柱外的神经元投射到粗条带和淡条带，这表明V1到V2的CO信息流存在功能特化。然而，传统的V1图谱显示所有第4B层神经元，无论其胞体位于斑块柱还是斑块间柱，都选择性地投射到L2/3层的CO斑块，这表明斑块/斑块间信息在L2/3层斑块以及可能的一些V2条带中汇聚。然而，尚不清楚所有第4B层投射神经元是否具有相似的局部神经回路。利用病毒介导的神经回路示踪技术，我们确定了猕猴中投射到V2粗条带的第4B层神经元的局部神经回路。与先前的研究一致，我们发现该第4B层亚群的胞体主要位于斑块柱之外；然而，与先前对第4B层局部神经回路的描述不同，这些细胞在所有层中始终投射到CO斑块柱之外。因此，这些第4B层输出神经元的局部神经回路，就像它们向V2的外在投射一样，保留了CO信息流。此外，V1内轴突投射的层内模式在该第4B层亚群中识别出两种不同的神经元类别，包括一种罕见的新型神经元类型，这暗示了两个功能特化的输出通道。
灵长类动物初级视觉皮层（V1）的传统图谱描绘了不同V1层内和层间的神经元连接，但缺乏有关细胞下游靶点的信息。这些信息对于理解V1中的局部处理如何与下游处理相关至关重要。我们确定了V1第4B层中投射到V2区的一群细胞的局部神经回路。这些细胞的局部神经回路在轴突靶向的层和功能区室方面与第4B层神经回路的经典描述不同，并识别出两种神经元类别。我们的结果表明，第4B层神经元的V1内局部连接和外在的V1到V2连接都保留了CO流分离，这表明跨流整合发生在V1下游，并且输出靶点决定了V1局部神经回路。
