Analysis of visual parameter processing and spatial information processing in the thalamofugal and tectofugal pathway of birds using high-dense electrodes

• Applicants: Professor Dr. Harald Luksch; Dr. Stefan Weigel
• Subject Area: Experimental and Theoretical Network Neuroscience
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 547075797

The processing of visual information is essential for orientation in space, but also to detect prey or predators. In vertebrates, two different processing pathways are distinguished: the tectofugal and the thalamofugal pathway. In the thalamofugal pathway, retinal ganglion cells (RGCs) topographically relay specific visual parameters to the nucleus geniculatum lateralis (birds: dorsal thalamus), which are distributed to different layers in the primary visual cortex (birds: visual Wulst). In the tectofugal pathway, the RGCs project to different sublayers of the superior colliculus (SC, birds: optic tectum). Functional classes of SC neurons project to different regions in the nucleus pulvinar (birds: nucleus rotundus, NRot). From there, information travels to striatal and extrastriatal forebrain areas (birds: entopallium). The ratio in the use of tectofugal and thalamofugal pathways in visual information processing varies between vertebrate groups; this probably depends on binocular overlap. These differences are also found between birds with laterally located eyes (e.g., chickens) and birds with frontal eyes (e.g., owls). It is unclear which retinal information is actually processed through each pathway. One hypothesis is that in the retinotectal pathway, during the transition from the optic tectum to the NRot, the sensory map of space is reduced to the visual parameters (functionotopy) with loss of spatial information. According to this hypothesis, the 'what' is encoded in the tectofugal pathway and the 'where' in the thalamofugal pathway. Other studies suggest that the processing is more complex and that the tecto- / thalamofugal pathway process different areas of the visual field and different visual parameters. To date, available morphological and physiological data in birds are inconclusive. We aim to verify visual processing in the tecto- & thalamofugal pathway using the chicken as a model system. Using multi-electrodes (Neuropixels 2.0) we want to perform a systematic mapping of the NRot and dorsal thalamus using different stimulus paradigms. Hereby, we want to clarify whether retinotopic information is indeed reduced in the nRot in favor of a pure mapping of function or whether retinotopy is preserved in the functional areas. Furthermore, we want to investigate which differences (visual field / parameters of visual information) exist in the processing of visual information across the thalamofugal and tectofugal pathways. Likewise, we want to clarify how simultaneously presented stimuli are mapped in the nRot when there is a reduction of spatial information.

• DFG Programme: Research Grants