Form in Darkness: Linking Visual Cortex Structure With Spontaneous Neural Function
Neuroscience and Neurobiology
Spontaneous neural activity within visual cortex is synchronized at varying spatial scales, from the cytoarchitecural level of individual neurons to the coarse scale of whole regions. The neural basis of this synchronicity remains ambiguous. In this thesis, we focus on the role visual experience plays in organizing the spontaneous activity within the visual system. We start in Chapter 2 by creating a means by which to analyze homologous patches of cortex between sighted and blind individuals, as lack of vision precludes the use of traditional stimulus-driven mapping techniques. We find that anatomy alone could indeed predict the retinotopic organization of an individual's striate cortex with an accuracy equivalent to the length of a typical mapping experiment. Chapter 3 applies this approach to analyze the organization of spontaneous signals within the striate cortex of blind and sighted subjects. We find that lack of visual experience produces a subtle change in the pattern of corticocortico correlations only between the hemispheres, and that these correlations are best modeled as function of cortical distance, not retinotopy. Chapter 4 expands our analysis to include areas V2 and V3. Here, we find that persistent visual experience supports network-level neural synchrony between spatially distributed cortical visual areas at both a coarse (regional) and fine (topographic) scale. Together, these results allow us model the organization of spontaneous activity in visual cortex as a combination of network signals linked to visual function and intrinsic signals coupled to structural connections. In the final chapter, we examine possible top-down mediators that may further modulate this network-level correlation. Minimal change in synchronicity is observed in a subject with a corpus callosotomy, suggesting the preeminence of bottom-up inputs. Taken together, this work advances our understanding of the origins of coherent spontaneous neural activity within visual cortex.