Functional Diversity of Retinal Ganglion Cells in the Rat
One of the central problems in neuroscience is that there is a lack of understanding of the diversity and functions of cell types in the brain. Even in brain areas that have been studied extensively, such as the retina, much remains to be learned about the diversity and functions of cell types. Morphological, functional and genetic studies have yet to converge on a consistent picture of cell type diversity in the retina, because the field lacks a standardized approach to classify cell types. A systematic classification approach is essential to provide an unambiguous appreciation of cell type diversity, and a better understanding of the organization and function of the retina. In the first portion of this dissertation, we present a novel approach that classifies retinal ganglion cells (RGCs) in a quantitative, verifiable and reproducible manner. We utilize diverse visual stimuli and a multi-electrode array, to record simultaneously from multiple RGCs, and show that there are at least 13 RGC types with distinct functional properties. In the second portion of the dissertation, we present a quantitative determination and comparison of the spatiotemporal receptive field (RF) structures and neural coding properties across these RGC types. Determining the RF structure of RGC types is important, because it constrains the computations performed by retinal circuits and identifies the signals available to retinal recipient areas. We find that RGC types exhibit functional asymmetries in terms of their RF size, temporal integration, and response nonlinearities. We also show that no RGC types exhibited RFs that were strictly independent in space and time. These results provide several new insights into the computations performed in the rodent retina, and highlight the importance of understanding cell type diversity to further our understanding of how the retina works and the role it plays in visual processing.
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