FUNCTIONAL TOPOGRAPHIC MAPPING OF THE CORTICAL RIBBON IN HUMAN VISIONWITH CONVENTIONAL MRI SCANNERS

THE human brain has anatomically distinct areas in which processing is laid out in space at the millimetre level with substantial variation across individuals. Activity occurs along a cortical ribbon 1.5-3 mm t hick1 in response to specific stimuli2,3. Here we report the first use of cortical ribbon analysis on humans using non-invasive functional m agnetic resonance imaging techniques performed with a conventional 1.5 T MRI scanner. Changes in activation were detected using T2-weighted , gradient echo imaging sequences. Subjects observed partial field, fl ashing checkerboard patterns (left-right, top-bottom, half rings, and wedges). Stimuli produced magnetic resonance signal changes in the 1-8 % range, varying at the millimetre scale, which showed contralateral v ertically reflected patterns of activation in the visual cortex. To co mpare the spatial topographies across subjects, computer algorithms we re used to control for the subject-unique folding of cortex, providing a flattened cortical ribbon identifying four topographically distinct areas.