Malach R
Center for Neurosciences and Behavioural Research, Weizmann Institute of Science, Rehovot, Israel.
J Neurosci. 1989 Nov;9(11):3741-52. doi: 10.1523/JNEUROSCI.09-11-03741.1989.
The definition of visual areas is one of the central problems in visual cortex research. Rodent extrastriate cortex offers a striking example of the complexity of this issue, in that different parcelation schemes identify within it from 2 to as many as 13 separate visual areas. In the experiments reported here, patterns of connections within rat visual cortex were studied in an effort to better define its organizational layout. The experimental paradigm used consisted of the following steps: first, the pattern of callosal connections was revealed in vivo with the fluorescent tracer bisbenzimide. Then, using the callosal pattern as a landmark, single injections of WGA-HRP were placed at various sites in striate and extrastriate cortex. Subsequently, the relation between the tangential distribution of ipsilateral corticocortical connections, the callosal connections, and the borders of striate cortex were examined in the flattened cortex preparation. The experiments revealed widespread, patchy connections within rat visual cortex. These connections appeared to reflect 3 organizational trends. First, neighboring sites were more extensively connected than distant ones. Second, extrastriate sites receiving common striate cortex inputs tended to be interconnected. Finally, projections from opposite poles in striate cortex tended to form interdigitating patterns of connections in regions of overlap. Altogether these trends suggest that the extrastriate band adjoining striate cortex has a single, global map organization. However, within the global map, a clear modular organization was evident, which appeared to correspond to the multiple visuotopic representations reported for this region. Based on its location, and some organizational similarities. it is suggested that the global map may constitute the rat homolog of area V2 in cat and monkey.
视觉区域的定义是视觉皮层研究中的核心问题之一。啮齿动物的纹外皮层为这个问题的复杂性提供了一个显著的例子，因为不同的分区方案在其中识别出2到多达13个不同的视觉区域。在本文报道的实验中，研究了大鼠视觉皮层内的连接模式，以更好地确定其组织结构布局。所采用的实验范式包括以下步骤：首先，用荧光示踪剂双苯甲酰胺在活体中揭示胼胝体连接模式。然后，以胼胝体模式为标志，将WGA-HRP单次注射到纹状皮层和纹外皮层的不同部位。随后，在扁平皮层标本中检查同侧皮质-皮质连接的切线分布、胼胝体连接与纹状皮层边界之间的关系。实验揭示了大鼠视觉皮层内广泛的、斑块状的连接。这些连接似乎反映了三种组织趋势。首先，相邻位点比远处位点的连接更广泛。其次，接受共同纹状皮层输入的纹外位点往往相互连接。最后，纹状皮层相对两极的投射往往在重叠区域形成相互交错的连接模式。总的来说，这些趋势表明，毗邻纹状皮层的纹外带具有单一的全局图谱组织。然而，在全局图谱中，明显存在清晰的模块化组织，这似乎与该区域报道的多个视拓扑表征相对应。基于其位置和一些组织上的相似性，有人提出全局图谱可能构成猫和猴V2区在大鼠中的同源物。
