Retinotopic organization in human visual cortex and the spatial precision of functional MRI

TLDR

The study presents an fMRI method to map retinotopic organization in human visual cortex and assess its spatial precision. The method uses a traveling‑wave visual stimulus to evoke retinotopic activity, records the resulting fMRI signal, and displays the data on flattened cortical maps. The technique delineated borders of several visual areas, mapped eccentricity in V1, localized activity to within 1.1 mm, and revealed an fMRI spatial resolution of ~3.5 mm (signal drops to 60 % at 1 cycle/9 mm).

Abstract

A method of using functional magnetic resonance imaging (fMRI) to measure retinotopic organization within human cortex is described. The method is based on a visual stimulus that creates a traveling wave of neural activity within retinotopically organized visual areas. We measured the fMRI signal caused by this stimulus in visual cortex and represented the results on images of the flattened cortical sheet. We used the 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 field 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 resolution is consistent with a linespread whose full width at half maximum spreads across 3.5 mm of visual cortex.