Burkhalter A, Bernardo K L, Charles V
Department of Neurology and Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri 63110.
J Neurosci. 1993 May;13(5):1916-31. doi: 10.1523/JNEUROSCI.13-05-01916.1993.
How we see the world largely depends on the organization of neuronal circuits in visual cortex. Physiological recordings in mammals indicate that circuits develop over a period that extends well into early postnatal ages (LeVay et al., 1980; Albus and Wolf, 1984). Our understanding of how these circuits are assembled during development is still fragmentary (Katz and Callaway, 1992). Here we describe the development of local connections within visual cortex, using the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate to trace axonal projections in post-mortem human brains. Vertical (intracolumnar) connections between layers 2/3 and 5, which link neurons representing the same point in the visual field, develop prenatally at 26-29 weeks gestation. In contrast, horizontal (intercolumnar) connections between different points in the visual field develop later. They first emerge prenatally at approximately 37 weeks gestation within layers 4B and 5. After birth (> 40 weeks gestation) the fiber density increases rapidly, showing a uniform plexus of connections at 7 weeks postnatal. The more adult-like patchiness of the projection, however, emerges after 8 weeks postnatal. Long-range horizontal connections within layer 2/3 develop after the connections within layers 4B, 5, and 6. These connections emerge after 16 weeks postnatal, long after cytochrome oxidase blobs have developed, and reach mature from sometime before 15 months of age. Unlike the patchy horizontal projections within layers 4B and 5, which seem to develop through a process of collateral elimination, long-range projections within layer 2/3 are patchy from the outset and seem to develop with greater topographical precision. The finding that intracolumnar connections develop before intercolumnar projections suggests that circuits that process local features of a visual scene develop before circuits necessary to integrate these features into a continuous and coherent neural representation of an image. In addition, the sequential development of horizontal connections within layer 4B before those within layer 2/3 suggests that circuits that may be related to the processing channel for visual motion develop in advance of those that may be more intimately related to the processing of form, color, and precise stereoscopic depth.
我们如何看待世界在很大程度上取决于视觉皮层中神经回路的组织方式。哺乳动物的生理学记录表明，神经回路的发育时期会一直持续到出生后的早期阶段（勒维等人，1980年；阿尔布斯和沃尔夫，1984年）。我们对这些回路在发育过程中如何组装的理解仍然支离破碎（卡茨和卡拉韦，1992年）。在这里，我们描述了视觉皮层内局部连接的发育情况，使用荧光染料1,1'-二辛基-3,3,3',3'-四甲基吲哚碳菁高氯酸盐来追踪死后人类大脑中的轴突投射。第2/3层和第5层之间的垂直（柱内）连接，连接着代表视野中同一点的神经元，在妊娠26 - 29周时产前发育。相比之下，视野中不同点之间的水平（柱间）连接发育较晚。它们首先在妊娠约37周时产前出现在第4B层和第5层内。出生后（妊娠> 40周），纤维密度迅速增加，在出生后7周时显示出均匀的连接丛。然而，投射更类似成人的斑块状在出生后8周后出现。第2/3层内的长程水平连接在第4B、5和6层内的连接之后发育。这些连接在出生后16周后出现，远在细胞色素氧化酶斑形成之后，并在15个月龄之前的某个时候达到成熟。与第4B层和第5层内斑块状的水平投射不同，后者似乎通过侧支消除过程发育，第2/3层内的长程投射从一开始就是斑块状的，并且似乎以更高的地形精度发育。柱内连接在柱间投射之前发育这一发现表明，处理视觉场景局部特征的回路在将这些特征整合为图像的连续且连贯的神经表征所需的回路之前发育。此外，第4B层内水平连接在第2/3层内水平连接之前的顺序发育表明，可能与视觉运动处理通道相关的回路比可能与形状、颜色和精确立体深度处理更密切相关的回路提前发育。
