RETINOTOPIC ORGANIZATION IN HUMAN VISUAL-CORTEX AND THE SPATIAL PRECISION OF FUNCTIONAL MRI

A method of using functional magnetic resonance imaging (fMRI) to meas ure retinotopic organization within human cortex is described. The met hod is based on a visual stimulus that creates a traveling wave of neu ral activity within retinotopically organized visual areas. We measure d the fMRI signal caused by this stimulus in visual cortex and represe nted the results on images of the flattened cortical sheet. We used th e method to locate visual areas and to evaluate the spatial precision of fMRI. Specifically, we: (i) identified the borders between several retinotopically organized visual areas in the posterior occipital lobe ; (ii) measured the function relating cortical position to visual fiel d eccentricity within area V1; (iii) localized activity to within 1.1 mm of visual cortex; and (iv) estimated the spatial resolution of the fMRI signal and found that signal amplitude falls to 60% at a spatial frequency of 1 cycle per 9 mm of visual cortex. This spatial resolutio n is consistent with a linespread whose full width at half maximum spr eads across 3.5 mm of visual cortex.