Cortical feedback microcircuits in the visual system of the mouse.

对外部世界的综合感知来自大脑皮层多个区域的感觉信息的处理。一般认为，多个皮质区域通过一个复杂的前馈和反馈连接网络相互连接。前向连接提供从较低区域到较高区域的信息，以便进一步(自下而上)处理。反馈连接从较高的区域发送信息并调节较低的区域的活动(自上而下)。根据这些类型的连接，提出了一个皮质处理的一般层次模型，并已应用于灵长类动物、猫和啮齿类动物。这些类型的皮质连接是由起源细胞及其终末轴突在大脑皮层6层的分布来定义的。轴突终末板层分布的这种大体模式是许多单一轴突的总和。对单个轴突的观察显示了各种终末模式，其中一些在前向和后向连接中都是常见的。对于构成这些皮质大回路的微回路，目前还没有深入的了解。经典的分层皮质网络模型最近受到了挑战，大脑皮层现在更多地被认为是一个分布式网络，而不是一个分层网络。越来越明显的是，皮质连接的二分分类不能解释广泛的连接类型。在局部水平上，有明确的证据表明皮质微循环将轴突的远程靶点反射到皮质和皮质下结构。本提案的目的是研究单个轴突水平的皮质连接的精细结构，以确定这些连接模式的构建块。在这样做的时候，我们将有一个基础来设计一种新的皮质连接分类，这将解释它们的多样性。我们还将提供这些长距离皮质连接如何与局部微电路相关的基本知识。

Integrated perception of the outside world emerges from the processing of sensory information in multiple areas of the cerebral cortex. It is generally believed that the multiple cortical areas are reciprocally interconnected by an intricate network of feedforward and feedback connections. Forward connections provide information from lower to higher areas for further (bottom-up) processing. Feedback connections send information from higher areas and modulate lower areas activity (top-down). From these types of connections a general hierarchical model of cortical processing has been proposed and has been applied to primates, cats and rodents. These types of cortical connections are defined by the distribution of the cells of origin and their terminal axons in the 6 layers of the cerebral cortex. This gross pattern of laminar distribution of axonal terminals is the result of the sum of a host of single axons. Observations of single axons show a variety of termination patterns some of which are common to both forward and backward connections. There is yet no in depth understanding of the microcircuits that constitute these cortical macrocircuits. The classical model of hierarchical cortical networks has recently been challenged and the cerebral cortex is now more perceived as a distributed rather than a hierarchical network. It is increasingly evident that a dichotomous classification of cortical connections cannot account for the broad spectrum of connection types. At a local level, there is clear evidence for cortical microcircuits that reflect the long range target of axons to cortical and subcortical structures. The objective of the present proposal is a study of the fine structure of corticocortical connections at the single axon level in order to define the building blocs of these connection patterns. In doing this, we will have the basis to devise a novel classification of cortical connection that will account for their diversity. We will also provide basic knowledge of how these long range cortical connections are related to local microcircuits.