The human brain needs to have access to an accurate map of visual space to interpret the images that we see. The most accurate and complete visual map is located in primary visual cortex, where all the basic stimulus properties are thought to be systematically represented, including spatial location, orientation and phase. For example, a vertical dark bar in the middle of this page can be represented in primary visual cortex by its position (point of fixation), orientation (vertical) and phase (dark flanked by light. While previous studies have made important advances in our understanding of how spatial location and orientation are mapped across the primary visual cortex, we still do not know how spatial phase is represented in this map. This is a fundamental gap in knowledge given the importance that phase has in image processing algorithms, which are regularly applied to satellite imagery, medical imaging, videophone and character recognition. Current experimental data suggest that spatial phase is randomly distributed throughout the cortex;however, computational models keep insisting that phase should be clustered in specific regions of the cortical map. Our recent results demonstrate, for the first time, the existence of pronounced clusters for spatial phase that are closely related to the mapping of stimulus orientation in cortex. In addition, we show that dark-dominated phases are better represented than light-dominated ones. The main goal of this research project is to study the organization of these newly discovered cortical maps for spatial phase with a novel approach that takes advantage of recent advances in multielectrode recording and has considerably better spatio-temporal resolution than other methods used in the past. With our multielectrode approach, we will reveal the inter- related organization of visual cortical maps for spatial position, orientation and phase the topography of dark- dominance in these maps and the rules that govern the representation of multiple stimulus dimensions within each 100 x 100 microns of cortex. We will use these measurements to build a detailed database of the multi- dimensional mapping of stimulus features across the visual cortical map and to test current computational models of functional cortical architecture and cortical development.
A complete understanding of how sensory maps are organized in the cerebral cortex is essential to guide future therapeutic approaches aimed at repairing or replacing cortical microcircuits. For example, the success of electrical neuronal prosthesis in the cerebral cortex not only require solving problems of tissue damage and electrode interphase but also requires a very detailed understanding of the cortical topography in which the prosthesis will be implanted. Interpreting the cortical changes that take place in visual disorders such as amblyopia and macular degeneration also requires a complete understanding of cortical map organization. Our research project is part of a maintained effort to reveal the functional organization of visual cortical maps, which will be needed to guide the treatments of insults to the visual brain in the future.
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