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Differential Encoding of Spatial Information among Retinal ON Cone Bipolar Cells
Date of Award
Doctor of Philosophy (PhD)
ON cone bipolar cells (ON CBCs) are retinal interneurons. They relay visual information from cone photoreceptors, the retina's input cells, to ganglion cells, the retina's output cells.
ON CBCs differ in the visual information they encode and subsequently relay. For example, some ON CBCs encode information about the timing of visual stimuli; others encode information about the chromaticity. The information an ON CBC encodes depends greatly on the complement of inputs it receives from cones, inhibitory horizontal cells, and inhibitory amacrine cells, as well as the complement of neurotransmitter receptors it possesses.
It is unknown whether spatial information is differentially encoded among ON CBCs as are temporal and chromatic information. We addressed this issue using single-cell electrophysiological methods, and found that it indeed is. Specifically, some ON CBCs were spatially tuned, encoding one stimulus size preferentially above all others. Other ON CBCs were not spatially tuned. This encoding dichotomy was a result of tuned ON CBCs receiving stronger inhibitory amacrine cell input than untuned ON CBCs. Additionally, a morphologic distinction was observed, with tuned cells having axonal arbors terminating more centrally in the inner plexiform layer than untuned cells.
Because the retina normally operates over a wide range of ambient light conditions, we examined how ambient illumination affected spatial information encoding among ON CBCs. The encoding dichotomy described above was diminished in bright ambient light, with all ON CBCs exhibiting significant spatial tuning. This was due to alterations of inhibitory amacrine cell input among ON CBCs.
Finally, we assessed whether spatial information encoded by ON CBCs reaches higher visual centers. We did so by examining whether ON CBCs relay spatial information to ganglion cells, the output cells of the retina. This was accomplished by recording from ganglion cells and reading out the ON CBC input they received. We found that ON CBCs indeed relayed spatial information to ganglion cells for presumable transmission to the brain.
In summary, ON CBCs encode spatial information for relay to ganglion cells. Their ability to do so varies with ambient illumination such that an encoding dichotomy exists in dim light, which diminishes in bright light.
Chair and Committee
James Huettner, Vladimir Kefalov, Daniel Kerschensteiner, Steven Mennerick, Robert Wilkinson
Purgert, Robert Joseph, "Differential Encoding of Spatial Information among Retinal ON Cone Bipolar Cells" (2015). Arts & Sciences Electronic Theses and Dissertations. 414.