Cortex-Wide Calcium Imaging of Visually Evoked Neural Population Activity in Mouse Visual Cortex
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Kim, Esther Kyuhae Kyuhae
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Abstract
The traditional method of electrophysiology provides neural activity measurements with cellular-level resolution, but it has limitations in probing neural activity across large spatial scales. Widefield imaging (WFI) of genetically engineered calcium-sensitive fluorescence proteins in neurons enables measurement of brain activity across large areas (~ 5 x 5 mm) with tens to hundreds millisecond scale resolution. In this thesis, we adapted an experimental and analytical framework with a WFI system for investigating visually evoked neural activity across the mouse visual cortex. We first validated identification of the primary visual cortex (V1) and higher visual areas (HVAs) through retinotopic mapping experiments. Calcium activities were then simultaneously measured across different visual areas in mice performing a visual detection task which involved visual processing of contrast and spatial features, and their profiles were characterized according to different performance. By performing region of interest (ROI) analysis based on the retinotopically registered images, we found that the response to the visual stimulus at different spatial locations of the ROI in the cortex were retinotopically specific. Also, we identified distinct calcium activity patterns between hit and miss trials, with hit trials showing contrast- dependent response modulation in the post-stimulus window, while miss trials displayed a bias towards higher baseline activity. Lastly, response magnitude and sensitivity is enhanced during the visual detection compared to passive visual perception. Further work such as optimizing the system functionality and employing efficient decomposition methods on the WFI data will reduce the variability in imaging data and provide more accurate understanding of network dynamics in visual and other cortical areas.
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2023-09-26
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