A three-dimensional functional investigation of the avian visual system - Do amniotes share a canonical forebrain circuit?

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

The visual systems of mammals and birds are highly evolved and specialized. In fact, many avian species surpass most mammals in spatial accuracy, temporal resolution and color sensitivity. Highly structured visual cortices, consisting of distinct layers with functional and anatomical ‘columns’, underlie mammalian vision. Instead, the avian visual system is organized in multiple clusters that resemble at the first glance the histological pattern known from the basal ganglia. Distinct layers or ‘columns’ are not immediately visible in birds. However, recent genetic data support the connectivity-based idea of a homology between distinct cortical layers and individual clusters of the avian sensory systems. Neuroanatomical data furthers this evolutionary similarity by demonstrating horizontal and vertical connectivity in the avian sensory systems that is akin to the canonical circuit of the mammalian cortex. Since it is unlikely that laminated and columnar organizations result from common ancestry, it is more likely that both vertebrate classes developed this pattern independently (convergent evolution) or sophisticated it in similar ways (parallel evolution) during 300 million years of separate evolution. We aim to investigate how these two principles of organization relate to each other and if they developed overlapping functional dynamics. We aim to 1. explore the three dimensional topography within each cluster of the avian tectofugal system. 2. analyze the different and possibly hierarchically organized coding principles and activity profiles within clusters and relate our results to known physiological dynamics of cortical layers and columns.3. investigate the presence of neural oscillations in the avian visual system. To date, we have no demonstration of the role of local field potentials in visual processing in the avian forebrain. Our mechanistic approach will give us a holistic understanding of the functional dynamics of the avian visual forebrain. This understanding will resolve if birds and mammals evolved comparable principles of neural processing in the form of a universal amniote canonical circuit.