Browsing by Author "Ravi, Sneha"
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Item Open Access Functional Diversity of Retinal Ganglion Cells in the Rat(2017) Ravi, SnehaOne 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.
Item Open Access Pathway-specific asymmetries between ON and OFF visual signalsRavi, Sneha; Ahn, Daniel; Greschner, Martin; Chichilnisky, EJ; Field, GregAbstractVisual processing is largely organized into ON and OFF pathways that signal stimulus increments and decrements, respectively. These pathways exhibit natural pairings based on morphological and physiological similarities, such as ON and OFF alpha ganglion cells in the mammalian retina. Several studies have noted asymmetries in the properties of ON and OFF pathways. For example, the spatial receptive fields (RFs) of OFF alpha cells are systematically smaller than ON alpha cells. Analysis of natural scenes suggests these asymmetries are optimal for visual encoding. To test the generality of ON-OFF asymmetries, we measured the spatiotemporal RF properties of multiple RGC types in rat retina. Through a quantitative and serial classification, we identified three functional pairs of ON and OFF RGCs. We analyzed the structure of their RFs and compared spatial integration, temporal integration, and gain across ON and OFF pairs. Similar to previous results from cat and primate, RGC types with larger spatial RFs exhibited briefer temporal integration and higher gain. However, each pair of ON and OFF RGC types exhibited distinct asymmetric relationships between receptive field properties, some of which were opposite to previous reports. These results reveal the functional organization of six RGC types in the rodent retina and indicate that ON-OFF asymmetries are pathway specific.Significance StatementCircuits that process sensory input frequently process increments separately from decrements, so called ‘ON’ and ‘OFF’ responses. Theoretical studies indicate this separation, and associated asymmetries in ON and OFF pathways, may be beneficial for encoding natural stimuli. However, the generality of ON and OFF pathway asymmetries has not been tested. Here we compare the functional properties of three distinct pairs of ON and OFF pathways in the rodent retina and show their asymmetries are pathway specific. These results provide a new view on the partitioning of vision across diverse ON and OFF signaling pathwaysItem Open Access Pathway-Specific Asymmetries between ON and OFF Visual Signals.(The Journal of neuroscience : the official journal of the Society for Neuroscience, 2018-11) Ravi, Sneha; Ahn, Daniel; Greschner, Martin; Chichilnisky, EJ; Field, Greg DVisual processing is largely organized into ON and OFF pathways that signal stimulus increments and decrements, respectively. These pathways exhibit natural pairings based on morphological and physiological similarities, such as ON and OFF α-ganglion cells in the mammalian retina. Several studies have noted asymmetries in the properties of ON and OFF pathways. For example, the spatial receptive fields (RFs) of OFF α-cells are systematically smaller than ON α-cells. Analysis of natural scenes suggests that these asymmetries are optimal for visual encoding. To test the generality of ON/OFF asymmetries, we measured the spatiotemporal RF properties of multiple RGC types in rat retina. Through a quantitative and serial classification, we identified three functional pairs of ON and OFF RGCs. We analyzed the structure of their RFs and compared spatial integration, temporal integration, and gain across ON and OFF pairs. Similar to previous results from the cat and primate, RGC types with larger spatial RFs exhibited briefer temporal integration and higher gain. However, each pair of ON and OFF RGC types exhibited distinct asymmetric relationships between RF properties, some of which were opposite to the findings of previous reports. These results reveal the functional organization of six RGC types in the rodent retina and indicate that ON/OFF asymmetries are pathway specific.SIGNIFICANCE STATEMENT Circuits that process sensory input frequently process increments separately from decrements, so-called ON and OFF responses. Theoretical studies indicate that this separation, and associated asymmetries in ON and OFF pathways, may be beneficial for encoding natural stimuli. However, the generality of ON and OFF pathway asymmetries has not been tested. Here we compare the functional properties of three distinct pairs of ON and OFF pathways in the rodent retina and show that their asymmetries are pathway specific. These results provide a new view on the partitioning of vision across diverse ON and OFF signaling pathways.