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枢感觉，因此，这两类动物的视觉系统都表现出显着的适应性和专门化。一个共性是，视觉信息沿着两条主要途径进行处理--丘脑分离途径和顶盖分离途径。然而，这些途径之间的分工差异很大，不仅在阶级之间，而且在每个阶级的不同物种之间也是如此。总的来说，视觉系统表现出高度的可变性和自适应性，这使得它成为神经处理进化优化研究的主要目标。在目前的应用中，我们将重点研究鸽子的丘脑分离视觉系统。由于我们对这一视觉通路的功能特性的大部分知识都来自猫头鹰--一种高级适应夜间捕食性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-分离系统。我们提出的系统探索允许从这一加工途径的一般特征中分离出物种特有的适应。与哺乳动物相比，关于鸟类丘脑逃逸通路中视觉信息处理的可用数据很少。此外，研究在使用的方法方面也各不相同。尤其是不同的刺激设置阻碍了直接比较。在我们的第一个项目中，我们继续对鸽子的技术分离视觉系统进行三维表征。我们的结果表明，所提出的这种视觉系统的皮质样解剖结构也体现在信息处理的生理学中。在接下来的项目中，我们为丘脑-分离性视觉系统提出了一种类似的方法。这为比较两种视觉系统对鸽子视觉处理的贡献提供了独特的机会--用相同的刺激和方法进行研究。除了视觉系统的功能特征外，该项目的目标是使用高密度电生理学和光遗传学操作来因果测试丘脑逃逸通路中的计算层次。我们将测试这样的假设，即丘脑分离的视觉系统与哺乳动物的皮质具有相同的解剖学和计算特性。在这里，我们对单个单位、局部场势及其振荡的系统记录，以及与我们在Göttingen的同事合作的信息论方法，将为不同水平的视觉信息处理提供深入的见解。在计算复杂性不断增加的分层组织结构中的视觉处理路径的收敛体系结构将暗示视觉能力的进化的有限自由度。

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.