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Pinglei Bao, Bosco S. Tjan; Spatial organization of spontaneous activities in the human visual cortex. Journal of Vision 2009;9(8):736. doi: https://doi.org/10.1167/9.8.736.
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© ARVO (1962-2015); The Authors (2016-present)
Spontaneous fluctuations in fMRI BOLD signal have been shown to be temporally correlated across widely distributed brain regions. We investigated the spontaneous fluctuations within the human visual cortex. A standard EPI sequence was used to acquire functional data (3mm isotropic voxels, TR = 1s). Subjects were scanned under a “rest” condition (eyes closed) and four fixation conditions, each consisted of a rotating wedge of high-contrast flickering checkerboard sweeping across one of the four halves of the visual field (upper, lower, left, right) during the entire run. A correlation-weighted cortical labeling method was used to reveal the spatial organization of the temporal coherency. Specifically, we designated a quadrant of V1 (e.g. ventral, left hemisphere) as the reference area, where each voxel was given a numeric label - either the eccentricity value or the polar angle from a separate retinotopy experiment. For a given voxel elsewhere on the cortex, we computed the temporal correlation between its spontaneous activities with those of each voxel in the reference area. The squared correlation coefficients were then combined with the reference labels to obtain a correlation-weighted label for the voxel in question. When eccentricity values were used as reference labels, the maps of correlation-weighted labels resembled eccentricity maps in all quadrants of all visual areas studied (V1, V2, V3) in the “rest” condition, across both horizontal and vertical meridians. The same was observed in the un-stimulated quadrants in the fixation conditions. Correlation-weighted labels continued to show a ring-like structure even when the reference region was stimulated by the rotating wedge or when polar angles were used as reference labels, suggesting that the correlations between spontaneous activities are strongly organized by eccentricity but remain non-specific in other spatial directions. This robust eccentricity organization of the spontaneous activities may reflect a fundamental organizational principle of the visual system.
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