THE DEVELOPMENT AND 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表现出来的，以及这些表现是如何在发育过程中形成的。在这方面研究得最好的皮质区域是V1和V2，其中视觉场景的位置、方向、方向和空间频率等特征以复杂的局部和全局结构的地图表示。了解这些地图是如何发展的，以及它们的最终结构背后的原则是回答上述问题的重要一步。遗传与表观遗传（特别是活动依赖）机制在决定视觉皮层结构中的相对作用仍然是一个激烈争论的主题。这一争论直接影响到设计有效的治疗方法来治疗早期视觉体验异常的影响，如斜视。视觉皮层图结构源于依赖于活动的学习规则，这些规则试图将高度相关的输入特征紧密地表示出来，并与基因决定的约束（如目标区域的形状）一起起作用。从传入活动的相关结构、皮质内连接模式和皮质靶区的形状之间的相互作用来看，V1和V2的局部和全局地图结构都可以解释。单眼剥夺、斜视等异常养育模式导致的图结构变化自然遵循相同的规律。该假设将使用适合探索大比例尺地图结构问题的计算模型进行测试。这些模型将应用于表示位置、方向、视觉优势、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，包括传入活动的统计结构的变化，皮质内连接模式的变化，输入特征之间的相似性测量方式的变化，以及目标区域形状的变化。在每个阶段，模拟结果将使用一系列定量技术直接与实验数据进行比较。这些计算模型的分析和模拟将导致关于皮层地图形成的参数和视觉经验对皮层地图结构的影响的实验可测试的预测。

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.