Topographic organization of human visual areas in the absence of input from primary cortex

Recently, there has been evidence for considerable plasticity in primary se nsory areas of adult cortex. In this study, we asked to what extent topogra phical maps in human extrastriate areas reorganize after damage to a portio n of primary visual (striate) cortex, V1. Functional magnetic resonance ima ging signals were measured in a subject (G.Y.) with a large calcarine lesio n that includes most of primary visual cortex but spares the foveal represe ntation. When foveal stimulation was present, intact cortex in the lesioned occipital lobe exhibited conventional retinotopic organization. Several vi sual areas could be identified (V1, V2, V3, V3 accessory, and V4 ventral). However, when stimuli were restricted to the blind portion of the visual fi eld, responses were found primarily in dorsal extrastriate areas. Furthermo re, cortex that had formerly shown normal topography now represented only t he visual field around the lower vertical meridian. Several possible source s for this reorganized activity are considered, including transcallosal con nections, direct subcortical projections to extrastriate cortex, and residu al inputs from V1 near the margin of the lesion. A scheme is described to e xplain how the reorganized signals could occur based on changes in the loca l neural connections.