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Alyssa Ann Brewer, Brian Barton, Ling Lin; A novel use for visual field maps: Tracking functional plasticity in posterior parietal cortex. Journal of Vision 2009;9(14):19. doi: https://doi.org/10.1167/9.14.19.
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“Introduction: Primate visual cortex can be partitioned into distinct visual areas which serve separate perceptual functions. One important organizing principle within many visual areas is a topographical map of visual space, also called a visual field map. The organization within these maps follows the organization of the retina; hence, retinotopic visual field maps are cortical regions in which nearby neurons analyze the properties of nearby points of an image on the retina. The ability to measure visual field maps in vivo, along with the stimulus selectivity of the various groups of neurons within these maps, is essential for understanding visual computations. In addition, knowledge of the normal organization of visual field maps allows us to study potential reorganization within visual cortex under conditions that may lead to a disruption of the normal inputs to these maps.
New visual field maps have recently been discovered in human posterior parietal cortex, a region that has been shown in human and monkey to be involved in the transformation of visual input into motor output. Here, by applying our cortical mapping techniques to the study of these maps along the intraparietal sulcus (IPS), we expand the definitions of these maps and show how they are organized into distinct clusters. We also investigate alterations in these visuomotor cortical maps as a person adapts to an extreme alteration of visual input created by left-right reversing prism goggles.
Methods: To first define these dorsal maps, we measured visual field representations using phase-encoded fMRI mapping methods. The rotating wedge and expanding ring stimuli consisted of 3, 7.4 and 11 deg black and white, drifting radial checkerboard patterns. In addition to these traditional traveling wave measurements, we also utilized a new method from Dumoulin and Wandell (2007) to measure the population receptive fields (pRFs) within individual cortical maps.
We then investigated whether these visual field maps in IPS change in response to alterations in visual input, as might be expected in a region involved in the dynamic mapping of visual space to motor output. Subjects underwent a two week continuous adaptation period to complete left-right visual field reversal. They performed a daily battery of visuomotor testing and training. Every 2–3 days, we made fMRI measurements of the cortical map organization and pRF distributions to track any changes in the representations of visual space within these maps.
Results: These retinotopic measurements illustrate multiple clusters of visual field maps along the IPS. The pRF sizes are larger in these maps than those measured in V1/V2/V3. Over the course of the two week adaptation period to the left-right reversal of the visual field, the fMRI and pRF measurements demonstrate a progressive shift of visual field representation from contralateral to ipsilateral visual space throughout the maps in IPS cortex. After returning visual input to normal, nearly all maps shift back to their baseline representations within 24 hours. Subjects initially perform very poorly on visuomotor behavioral tasks, but return to baseline performance by the end of the two week adaptation period.
Conclusions: These visual field map measurements identify and describe the cortical regions subserving the dynamic remapping of visuospatial representations in response to altered visual input.”
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