PERIODIC EXTRINSIC CONNECTIONS IN VISUAL CORTEX

纹外视皮层由多个不同的区域组成。 地形、解剖连通性和神经元反应特性。 行为-生理联合实验，与其他 研究表明，这些差异是功能上的 意义重大。特别是，它们被认为与 选择性地处理不同类型的可视信息(流)， 并代表感觉-知觉转换的不同阶段。 纹外肌生理变化的特征 大脑皮层仍处于早期阶段。某些总的趋势一直是 与初级视觉皮质相比观察到的；例如， 视网膜位置和刺激参数的特异性，以及 响应属性的复杂性增加。然而，仍然不清楚的是， 特定进程是否可能唯一地与给定的 区域，或者不同区域是否可以共享共同的计算策略。 阐明纹外区功能结构的一种方法 区域是调查一个区域的“布线”，就像系统地进行的那样 在V1区，在单个神经元和轴突水平上完成。现在 项目已经采用了这种方法，并从将小种群标记为 V1区带PHA-L的传出轴突在到目前为止的观察中，我们 报告1)皮质轴突不是刻板印象的。即使在一个单独的 投射焦点在V2区，单个轴突的数目和 在某种程度上，它们的终端集群的大小；2)虽然终端 V2区的乔木大小不一，大多数比 CO条纹的尺寸；3)虽然不是绝对的，但有 V2和MT的末端乔木的大小令人惊讶的恒定(即大约 200um)，但MT的总分支可能比V2的分化更大。 在下一个授权期，我们将1)定义PHA-L的末端基因座 标记的外轴突，从V1区到V2区，从V2区到V1区，在 与模块化结构的关系(表现为倒退的集群 通过CO组织化学标记神经元，或在V1中通过GABA免疫组织化学标记神经元。 反应性)；2)研究PHA-L标记的V2区至某些区域的轴突 外在皮质靶点，以及V2内；3)表征 皮质轴突传入MT区和不同脑区的超微结构 V2中的隔室，就生理显著特征而言，如 如轴突直径、终末特化的大小和密度；以及4) 开始通过超微结构研究轴突与靶细胞的相互作用 V2层V1轴突突触后成分的观察。 除了可能的功能相关性外，希望这一点 研究还将为未来的个体发育研究提供基线， 轴突树枝形成中的病理或活动相关的改变 超微结构，为大脑皮层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.