The adult brain has a remarkable ability to adjust to changes in sensory input. Removal of afferent input to the somatosensory, auditory, motor or visual cortex results in a marked change of cortical topography. Changes in sensory activity can, over a period of months, alter receptive field size and cortical topography. Here we remove visual input by focal binocular retinal lesions and record from the same cortical sites before and within minutes after making the lesion and find immediate striking increases in receptive field size for cortical cells with receptive fields near the edge of the retinal scotoma. After a few months even the cortical areas that were initially silenced by the lesion recover visual activity, representing retinotopic loci surrounding the lesion. At the level of the lateral geniculate nucleus, which provides the visual input to the striate cortex, a large silent region remains. Furthermore, anatomical studies show that the spread of geniculocortical afferents is insufficient to account for the cortical recovery. The results indicate that the topographic reorganization within the cortex was largely due to synaptic changes intrinsic to the cortex, perhaps through the plexus of long-range horizontal connections.