THE DEVELOPMENT & STRUCTURE OF VISUAL CORTICAL MAPS

理解视觉系统的两个关键问题是，关于世界的信息是如何在大脑皮层中呈现的，以及这些呈现是如何在发育过程中形成的。在这方面研究最多的是V1和V2，其中视觉场景的特征，如位置、方向、方向和空间频率在具有复杂的局部和全局结构的地图上表示。了解这些地图是如何发展的，以及它们最终结构的基础是什么原则，是回答上述问题的重要一步。遗传和表观遗传(尤其是依赖活动的)机制在决定视觉皮质结构中的相对贡献仍然是一个激烈辩论的主题。这场辩论直接影响到设计有效的治疗方法来治疗早期异常视觉体验的影响，如斜视。视觉大脑皮层地图结构源于依赖活动的学习规则，这些学习规则试图将高度相关的输入特征紧密地表示在一起，并与目标区域的形状等基因决定的约束相结合。V1和V2中MAP的局部和整体结构都可以根据传入活动的相关结构、皮质内连接的模式和皮质靶区的形状之间的相互作用来解释。由于单眼剥夺和斜视等异常养育范式导致的MAP结构的变化自然遵循相同的规则。这一假设将使用适合于探索大尺度地图结构问题的计算模型进行验证。这些模型将应用于表示位置、方向、眼睛优势、方向、空间频率、视差和颜色的低维特征空间。将研究几种类型的参数变化，包括传入活动统计结构的变化，皮质内连接模式的变化，输入特征之间相似性测量方式的变化，以及靶区形状的变化。在每个阶段，将使用一系列定量技术将模拟结果与实验数据直接进行比较。这些计算模型的分析和模拟将导致关于大脑皮层地图形成的参数和视觉经验对大脑皮层地图结构的影响的实验可检验的预测。

Two key questions for understanding the visual system are, how is information about the world represented in the cortex, and how are these representations formed during development. The best studied cortical areas in this regard are V1 and V2, where features of the visual scene such as position, orientation, direction and spatial frequency are represented in maps with complex local and global structure. Understanding how these maps develop, and what principles underlie their final structure, is an important step in answering the above questions. The relative contribution of genetic versus epigenetic (particularly activity-dependent) mechanisms in determining visual cortical structure is still a subject of intense debate. This debate impacts directly on the design of effective therapies for treating the effects of early abnormal visual experience, such as strabismus. Visual cortical map structure arises from activity-dependent learning rules that attempt to represent highly correlated input features close together, acting in conjunction with genetically determined constraints such as the shape of the target area. Both the local and global structure of maps in V1 and V2 can be accounted for in terms of the interaction between the correlational structure of afferent activity, patterns of intracortical connections, and the shape of the cortical target region. Changes in map structure due to abnormal rearing paradigms such as monocular deprivation and strabismus follow naturally from the same rules. The hypothesis will be tested using computational models suited to exploring questions of large scale map structure. These models will be applied to low dimensional feature spaces representing position, orientation, ocular dominance, direction, spatial frequency, disparity, and color. Several types of parameter variation will be investigated, including variations in the statistical structure of afferent activity, variations in the pattern of intracortical connections, variations in the way similarity between input features is measured, and variations in the shape of the target region. At each stage, simulation results will be directly compared to experimental data using a range of quantitative techniques. The analysis and simulation of these computational models will lead to experimentally testable predictions concerning the parameters underlying cortical map formation and the effects of visual experience on cortical map structure.