Abstract
When neurons in primary visual cortex of adult cats and monkeys are deprived of their normal sources of activation by matching lesions in the two retinas, they are capable of acquiring new receptive fields based on inputs from regions of intact retina around the lesions. Although these “reactivated” neurons respond to visual stimuli, quantitative studies of their response characteristics have not been attempted. Thus, it is not known whether these neurons have normal or abnormal features that could contribute to or disrupt an analysis of a visual scene. In this study, we used extracellular single-unit recording methods to investigate their stimulus selectivity and responsiveness. Specifically, we measured the sensitivity of individual neurons to stimulus orientation, direction of drift, spatial frequency, and contrast. Over 98% of all units in the denervated zone of cortex acquired new receptive fields after 3 months of recovery. Newly activated units exhibited strikingly normal orientation tuning, direction selectivity, and spatial frequency tuning when high-contrast (< 40%) stimuli were used. However, contrast thresholds of most neurons were abnormally elevated, and the maximum response amplitude under optimal stimulus conditions was significantly reduced. The results suggest that the striate cortical neurons reactivated during topographic reorganization are capable of sending functionally meaningful signals to more central structures provided that the visual scene contains relatively high contrast images.
