Auditory Compensation for Early Blindness in Cat Cerebral Cortex

Single-neuron activity was recorded in the caudal part of the anterior ectosylvian (AE) cortex of cats that had been deprived of vision for several years by means of binocular lid suture shortly after birth and in normal control animals. Over 300 neurons were tested in each group with auditory, visual, and somatosensory stimuli. We confirmed the existence of an anterior ectosylvian visual area (AEV) in the fundus and ventral bank of the AE sulcus. Neurons in AEV had purely visual responses in normal cats. In visually deprived cats, by contrast, only a minority of cells in this area still responded to visual stimulation. Instead, most cells reacted vigorously to auditory and, to some extent, somatosensory stimuli. The few remaining visual neurons were also driven by auditory or somatosensory stimuli. No increase in the number of unresponsive neurons was found. It appears, therefore, that a cortical region that normally represents visual activity can become driven by auditory or somatosensory activity as a result of visual deprivation. Our results imply that early blindness causes compensatory increases in the amount of auditory cortical representation, possibly by an expansion of nonvisual areas into previously visual territory. In particular, they provide evidence for the existence of neural mechanisms for intermodal compensatory plasticity in the cerebral cortex of young animals. The changes described here may also provide the neural basis for a behavioral compensation for early blindness described elsewhere.