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Petya D. Radoeva, Geoffrey K. Aguirre; Representation of the ipsilateral visual field in early retinotopic cortex. Journal of Vision 2007;7(9):225. doi: 10.1167/7.9.225.
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© ARVO (1962-2015); The Authors (2016-present)
Early visual areas contain neurons responsive to stimuli in the contralateral visual field. At higher levels of the visual hierarchy, neurons with receptive fields that cross the midline are identified. The recovery from cortical injury in other sensory and effector modalities is associated with development or unmasking of responsiveness to the ipsilateral (contralesional) side. In preparation for studies of recovery of visual function following visual pathway lesions, we quantified the normative responsiveness of retinotopically organized visual areas to the ipsilateral visual field. Six subjects participated in fMRI scanning sessions during which polar angle and eccentricity mapping stimuli were presented in isolation to each visual hemifield. All reflective surfaces within the scanner bore and head coil were covered with black cloth or matte tape to eliminate the scatter of light to the other visual hemifield. In preliminary data analyses from two subjects, visual areas were identified on the flattened cortical sheet of each hemisphere by polar angle stimuli presented to the contralateral visual field. In all four hemispheres, voxels with modulation of response by the ipsilateral visual field were identified within areas V1, V2, V3 and hV4. We then examined the correlation between the ipsi- and contralateral peak eccentricity response in these voxels. Amongst early visual areas, area hV4 showed a strong correlation, with R^2 values of approximately 0.5 and greater, and slopes approaching unity. Significant, but far weaker, correlations were observed in V1 and V2/V3. Ongoing analyses will examine the relative contribution of near vs. far periphery responses and the degree to which responsiveness to polar angle is shared across the visual fields.
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