A three-dimensional investigation of the avian thalamofugal visual system –Functional properties, relation to the avian tectofugal system and comparison to the mammalian cortex

视觉是大多数鸟类和哺乳动物的中心感官，因此这两类动物的视觉系统都表现出显著的适应性和专业化。一个共同点是，视觉信息是通过两条主要途径处理的——丘脑通道和构造通道。然而，这些途径之间的分工差异很大，不仅在类之间，而且在每个类的不同物种之间。一般来说，视觉系统似乎是高度可变和自适应的，使其成为神经处理进化优化研究的主要目标。在目前的应用中，我们将重点关注鸽子的丘脑视觉系统。由于我们对这条视觉通路的功能特性的大部分知识来自猫头鹰——一种具有先进的适应夜间捕食生活方式的视觉专家——我们的目标是研究多面手鸽子的丘脑系统。我们提出的系统探索允许从这种加工途径的一般特征中分离出物种特异性适应。与哺乳动物相比，关于鸟类丘脑通道中视觉信息处理的可用数据很少。此外，这些研究在使用的方法方面也有所不同。特别是不同的刺激集阻碍了直接比较。在我们的第一个项目中，我们继续对鸽子的构造视觉系统进行三维表征。我们的研究结果表明，这种视觉系统的皮层样解剖结构也体现在信息处理的生理学中。在即将到来的项目中，我们提出了一个类似的丘脑视觉系统的方法。这提供了一个独特的机会来比较两种视觉系统对鸽子视觉处理的贡献——用相同的刺激和方法进行研究。除了视觉系统的功能表征之外，该项目还旨在使用高密度电生理学和光遗传学操作来测试丘脑通路内的计算层次。我们将测试丘脑视觉系统与哺乳动物皮质共享解剖学和计算特性的假设。在这里，我们系统地记录单个单元，局部场电位及其振荡，以及与Göttingen的同事合作的信息理论方法，将为不同层次的视觉信息处理提供见解。在计算复杂度不断增加的分层组织结构中，视觉处理路径的趋同架构将暗示视觉能力进化的自由度有限。

Vision is a central sense for most birds and mammals and consequently the visual systems of both classes show remarkable adaptations and specializations. A commonality is that visual information is processed along two main pathways – the thalamofugal and the tectofugal pathway. However, the division of labor between these pathways varies substantially, not only between the classes but also between the different species of each class. In general, the visual system appears to be highly variable and adaptive making it a prime target for the investigation of the evolutionary optimization of neural processing. In the current application, we will focus on the thalamofugal visual system of the pigeon. Since the majority of our knowledge on the functional properties of this visual pathway stems from owls – an order of visual specialists with advanced adaptations for a nocturnal predatory lifestyle – we aim to investigate the thalamofugal system of the generalist pigeon. Our proposed systematic exploration allows disentangling species-specific adaptations from general features of this processing pathway. In comparison to mammals, there are only few available data on the processing of visual information in the avian thalamofugal pathway. In addition, the studies varied with respect to the methods used. Especially different stimulus sets used hinder a direct comparison. In our first project, we are continuing to perform a three dimensional characterization of the pigeons’ tectofugal visual system. Our results suggest, that the proposed cortex-like anatomy of this visual system is also represented in the physiology of information processing. In the upcoming project, we propose a comparable approach for the thalamofugal visual system. This provides the unique opportunity to compare the contribution of both visual systems – investigated with the same stimuli and methods – to visual processing in pigeons. Beyond the functional characterization of the visual system, the project aims to causally test the computational hierarchy within the thalamofugal pathway using high-density electrophysiology as well as optogenetic manipulations. We will test the hypothesis that the thalamofugal visual system shares anatomical and computational properties with the mammalian cortex. Here our systematic recording of single units, local field potentials and their oscillations as well as an information theoretic approach in cooperation with our colleagues in Göttingen, will give insights into the processing of visual information at different levels. A convergent architecture of visual processing pathways in hierarchically organized structures with increasing complexity in their computations would hint to limited degrees of freedom for the evolution of visual capabilities.