PERIODIC EXTRINSIC CONNECTIONS IN VISUAL CORTEX

纹状体外视皮层由多个区域组成，这些区域的功能各不相同。 拓扑学、解剖学连接性和神经元响应特性。 结合行为-生理学实验，结合其他 研究表明，这些差异是 显著 特别是，它们被认为与 不同类型的可视信息（“流”）的选择性处理， 并代表感觉-知觉转换中的不同阶段。 纹状体外神经元的生理变化特征 大脑皮层仍处于早期阶段。 某些普遍的趋势 与初级视觉皮层形成对比;例如， 视网膜位置和刺激参数的特异性，沿着 增加了响应特性的复杂性。 不过，还不清楚的是 特定进程是否唯一地与给定的 区域，或者不同的区域是否可以共享共同的计算策略。 阐明纹状体外神经功能构筑的一种方法 区域是调查一个区域的“布线”，因为已经系统地 在V1区，在单个神经元和轴突的水平上完成。 本 这个项目采用了这种方法，首先是给一小部分人群贴上 PHA-L从V1区传出的轴突。 在迄今为止的观察中，我们 报道1）皮质轴突不是定型的。 即使在单个 投影聚焦在区域V2中，单个轴突的数量和 在一定程度上，它们的终端集群的大小; 2）虽然终端 在区域V2中，心轴的尺寸不同，大多数小于（约200 μ m） CO条纹的尺寸; 3）尽管不是绝对的， V2和MT中的末端轴的令人惊讶的尺寸恒定性（即，关于 200 μ m），但MT的总树枝状结构可能比V2更分散。 在下一个资助期，我们将1）确定PHA-L的末端基因座 标记的外源性轴突，从V1区到V2区，以及从V2区到V1区，在 与模块化结构的关系（通过一簇逆行的 标记的神经元，通过CO组织化学，或在V1，通过GABA-免疫组织化学 2）研究PHA-L标记的轴突从V2区到 外源性皮质靶点，以及V2内; 3）表征 传出MT区和不同MT区的超微结构皮质轴突 V2中的隔室，在生理学显著特征方面，例如 轴突直径、末端特化的大小和密度;以及4） 开始研究轴突-靶细胞相互作用的超微结构 V2第3层和第4层中V1轴突突触后成分的调查。 除了可能的职能相关性外，希望这一点 这项研究也将为将来研究个体发生、发育和演化提供一个基线， 轴突树枝状结构中的病理或活动相关改变，以及 超微结构的研究，为脑皮质超微结构的理论建模提供数据 功能

Extrastriate visual cortex is made up of multiple areas differing in their topography, anatomical connectivity, and neuronal response properties. Combined behavioral-physiological experiments, in conjunction with other lines of research, suggest that these differences are functionally significant. In particular, they are thought to be associated with selective processing of different types of visual information ("streams"), and to represent different stages in sensory-perceptual transformations. The characterization of physiological transformations in extrastriate cortex is still at an early stage. Certain general tendencies have been observed in contrast with primary visual cortex; for example, a decrease in specificity for retinal position and stimulus parameters, along with an increased complexity in response properties. Still not clear, however, is whether particular processes might be uniquely associated with a given area, or whether different areas may share common computational strategies. One approach to elucidating the functional architecture of extrastriate areas is to investigate the "wiring" of an area, as has systematically been done in area V1, at the level of single neurons and axons. The present project has taken this approach, and begun by labeling small populations f efferent axons from area V1 with PHA-L. Among observations to date, we report 1) that cortical axons are not stereotyped. Even within a single projection focus in area V2, individual axons vary in the number and, to some extent, the size of their terminal clusters; 2) although terminal arbors vary in size in area V2, the majority are smaller (about 200um) than the dimensions of CO stripes; and 3) although not absolute, there is surprising size constancy of terminal arbors in both V2 and MT (i.e., about 200um), but total arborizations may be more divergent in MT than in V2. In the next grant period, we will 1) define the terminal loci of PHA-L labeled extrinsic axons, from area V1 to V2, and from area V2 to V1, in relation to modular structure (demonstrated by clusters of retrogradely labeled neurons, by CO histochemistry, or, in V1, by GABA-immuno- reactivity); 2) investigate PHA-L labeled axons from area V2 to certain extrinsic cortical targets, as well as within V2; 3) characterize ultrastructurally cortical axons efferent to area MT and to different compartments in V2, in terms of physiologically significant features such as axon diameter, and size and density of terminal specializations; and 4) begin to investigate axon-target cell interactions by an ultrastructural survey of elements postsynaptic to V1 axons in layers 3 and 4 of V2. In addition to possible functional relevance, it is hoped that this research will also provide a baseline for future studies on ontogenetic, pathological, or activity-related modifications in axonal arborization and ultrastructure, and provide data for theoretical modeling of cortical function.