Amir Y, Harel M, Malach R
Weizmann Institute of Science, Rehovot, Israel.
J Comp Neurol. 1993 Aug 1;334(1):19-46. doi: 10.1002/cne.903340103.
Neuronal response properties vary markedly at increasing levels of the cortical hierarchy. At present it is unclear how these variations are reflected in the organization of the intrinsic cortical circuitry. Here we analyze patterns of intrinsic horizontal connections at different hierarchical levels in the visual cortex of the macaque monkey. The connections were studied in tangential sections of flattened cortices, which were injected with the anterograde tracer biocytin. We directly compared the organization of connections in four cortical areas representing four different levels in the cortical hierarchy. The areas were visual areas 1, 2, 4 and Brodman's area 7a (V1, V2, V4 and 7a, respectively). In all areas studied, injections labeled numerous horizontally coursing axons that formed dense halos around the injection sites. Further away, the fibers tended to form separate clusters. Many fibers could be traced along the way from the injection sites to the target clusters. At progressively higher order areas, there was a striking increase in the spread of intrinsic connections: from a measured distance of 2.1 mm in area V1 to 9.0 mm in area 7a. Average interpatch distance also increased from 0.61 mm in area V1 to 1.56 mm in area 7a. In contrast, patch size changed far less at higher order areas, from an average width of 230 micron(s) in area V1 to 310 micron(s) in area 7a. Analysis of synaptic bouton distribution along axons revealed that average interbouton distance remained constant at 6.4 micron(s) (median) in and out of the clusters and in the different cortical areas. Larger injections resulted in a marked increase in the number of labeled patches but only a minor increase in the spread of connections or in patch size. Thus, in line with the more global computational roles proposed for the higher order visual areas, the spread of intrinsic connections is increased with the hierarchy level. On the other hand, the clustered organization of the connections is preserved at higher order areas. These clusters may reflect the existence of cortical modules having blob-like dimensions throughout macaque monkey visual cortex.
在皮质层级不断升高的过程中，神经元的反应特性存在显著差异。目前尚不清楚这些差异是如何在皮质内在神经回路的组织中体现出来的。在此，我们分析了猕猴视觉皮质不同层级水平上的内在水平连接模式。通过向扁平皮质的切线切片中注射顺行示踪剂生物素，对这些连接进行了研究。我们直接比较了代表皮质层级中四个不同水平的四个皮质区域内连接的组织情况。这些区域分别是视觉区域1、2、4和布罗德曼7a区（分别为V1、V2、V4和7a）。在所研究的所有区域中，注射标记了大量水平走行的轴突，这些轴突在注射部位周围形成了密集的光环。在更远的地方，纤维倾向于形成单独的簇。许多纤维可以从注射部位一直追踪到目标簇。在层级逐渐升高的区域中，内在连接的扩散有显著增加：从V1区测量的2.1毫米距离增加到7a区的9.0毫米。平均斑块间距离也从V1区的0.61毫米增加到7a区的1.56毫米。相比之下，在层级较高的区域中，斑块大小的变化要小得多，从V1区的平均宽度230微米增加到7a区的310微米。对沿轴突的突触小体分布进行分析表明，平均突触小体间距在簇内外以及不同皮质区域中均保持恒定，为6.4微米（中位数）。更大的注射导致标记斑块数量显著增加，但连接扩散或斑块大小仅有轻微增加。因此，与为更高层级视觉区域所提出的更全局的计算作用一致，内在连接的扩散随着层级水平的升高而增加。另一方面，连接的簇状组织在层级较高的区域中得以保留。这些簇可能反映了整个猕猴视觉皮质中存在具有斑点状尺寸的皮质模块。
