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Xin-Lin Goh, Andrew C. James, Linda Henriksson, Simo Vanni; Multifocal 60 region fMRI derivation of the 3D structure and magnification factor of human primary visual cortex. Journal of Vision 2005;5(8):890. doi: https://doi.org/10.1167/5.8.890.
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© ARVO (1962-2015); The Authors (2016-present)
Results are presented here from the multifocal FMRI analysis of human primary visual cortex, which derives activation maps for 60 fixed visual field locations by decomposition of the compound response to test stimulus sequences applied concurrently to each location. The stimulus layout was a 60 region cortically-scaled dartboard of diameter 24o comprising 12 sectors in each of 5 concentric rings scaled to activate approximately equal areas in cortical area V1. For each 7.2 second block of the run, a different set of half of the 60 regions was active with 4×4 checkerboards reversing at 8 reversals/s, according to an orthogonal design. Two runs of 8 minutes give adequate results. Six subjects had scans done in a 3T GE Signa scanner, along with structural MRI and phase-encoded retinotopic analysis of conventional design. Data were analyzed with SPM2 with custom extensions to optimally estimate activation strength and significance maps for each of the 60 stimulus regions. Calculation of the centre of mass of the thresholded volume distributions for each of the 60 visual field regions produces robust 3D localization of the centre of primary visual cortex response for each stimulus region, in all subjects. The 30 points in each hemisphere produce surfaces in 3D reliably mapping primary visual cortex in and around the calcarine sulcus. The surfaces obtained are in agreement with the white matter-gray matter border derived from segmentation of high-resolution anatomical scans, but can be derived without them. Thin-plate splines were used to fit smooth surfaces through the primary 3D data, from which estimates of the cortical magnification factor are derived with respect to eccentricity and polar angle, and compared with current models. The viability of detailed mapping of the 3D structure of human primary visual cortex without requiring co-registration with high resolution anatomical data is demonstrated.
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