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

Onur Güntürkün – Ruhr-Universität Bochum
Roland Pusch – Ruhr-Universität Bochum
Jonas Rose – Ruhr-Universität Bochum

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.