Alonso J M, Usrey W M, Reid R C
Laboratory of Neurobiology, The Rockefeller University, New York, New York 10021, USA.
J Neurosci. 2001 Jun 1;21(11):4002-15. doi: 10.1523/JNEUROSCI.21-11-04002.2001.
Hundreds of thalamic axons ramify within a column of cat visual cortex; yet each layer 4 neuron receives input from only a fraction of them. We have examined the specificity of these connections by recording simultaneously from layer 4 simple cells and cells in the lateral geniculate nucleus with spatially overlapping receptive fields (n = 221 cell pairs). Because of the precise retinotopic organization of visual cortex, the geniculate axons and simple-cell dendrites of these cell pairs should have overlapped within layer 4. Nevertheless, monosynaptic connections were identified in only 33% of all cases, as estimated by cross-correlation analysis. The visual responses of monosynaptically connected geniculate cells and simple cells were closely related. The probability of connection was greatest when a geniculate center overlapped a strong simple-cell subregion of the same sign (ON or OFF) near the center of the subregion. This probability was further increased when the time courses of the visual responses were similar. In addition, the connections were strongest when the simple-cell subregion and the geniculate center were matched in position, sign, and size. The rules of connectivity between geniculate afferents and simple cells resemble those found for retinal afferents to geniculate cells. The connections along the retinogeniculocortical pathway, therefore, show a precision that goes beyond simple retinotopy to include many other response properties, such as receptive-field sign, timing, subregion strength, and size. This specificity in wiring emphasizes the need for developmental mechanisms (presumably correlation-based) that can select among afferents that differ only slightly in their response properties.
数百条丘脑轴突在猫的视皮层的一个柱状结构内分支；然而，每个第4层神经元仅从其中一部分接收输入。我们通过同时记录第4层简单细胞和外侧膝状体核中具有空间重叠感受野的细胞（n = 221个细胞对）来研究这些连接的特异性。由于视皮层精确的视网膜拓扑组织，这些细胞对的膝状体轴突和简单细胞树突应该在第4层内重叠。然而，通过互相关分析估计，在所有情况中只有33%鉴定出单突触连接。单突触连接的膝状体细胞和简单细胞的视觉反应密切相关。当膝状体中心与同一符号（开或关）的强简单细胞子区域在子区域中心附近重叠时，连接的概率最大。当视觉反应的时间进程相似时，这种概率会进一步增加。此外，当简单细胞子区域和膝状体中心在位置、符号和大小上匹配时，连接最强。膝状体传入纤维与简单细胞之间的连接规则类似于视网膜传入纤维与膝状体细胞之间的连接规则。因此，沿视网膜 - 膝状体 - 皮质通路的连接显示出一种精确性，这种精确性超越了简单的视网膜拓扑，还包括许多其他反应特性，如感受野符号、时间、子区域强度和大小。这种布线的特异性强调了对发育机制（可能基于相关性）的需求，这些机制可以在反应特性仅略有不同的传入纤维之间进行选择。
