Cortical feedback microcircuits in the visual system of the mouse.

外部世界的综合知觉来自于大脑皮层多个区域对感觉信息的处理。一般认为，多个皮层区域是通过一个复杂的前馈和反馈连接网络相互连接的。前向连接提供从较低区域到较高区域的信息，以便进一步（自底向上）处理。反馈连接从高级区域发送信息并调节低级区域的活动（自上而下）。从这些类型的连接中提出了一个皮层处理的一般层次模型，并已应用于灵长类动物，猫和啮齿动物。这些类型的皮层连接是由起源细胞及其终端轴突在大脑皮层6层中的分布来定义的。这种轴突终末层流分布的大体模式是许多单个轴突总和的结果。对单个轴突的观察显示出多种终止模式，其中一些是前向和后向连接所共有的。目前对构成这些皮质巨回路的微电路还没有深入的了解。分层皮层网络的经典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的而不是一个分层的网络。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，皮层微回路反映了轴突到皮层和皮层下结构的远距离目标。本研究的目的是在单轴突水平上研究皮质皮质连接的精细结构，以确定这些连接模式的构建块。在此过程中，我们将有基础设计一种新的皮层连接分类，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.