In mammals, neurons in the brain that process vision actually develop after birth based on signals from the eyes. A landmark experiment by David H. Hubel and Torsten Wiesel (1963) showed that cats that had one eye sewn shut from birth to three months of age (monocular deprivation) only fully developed vision in the open eye. They showed that columns in the primary visual cortex receiving inputs from the other eye took over the areas that would normally receive input from the deprived eye. In general electrophysiological analyses of axons and neurons in the lateral geniculate nucleus showed that the visual receptive field properties was comparable to adult cats. However, the layers of cortex that were deprived had less activity and fewer responses were isolated. The kittens had abnormally small ocular dominance columns (part of the brain that processes sight) connected to the closed eye, and abnormally large, wide columns connected to the open eye. Because the critical period time had elapsed, it would be impossible for the kittens to alter and develop vision in the closed eye. This did not happen to adult cats even when one eye was sewn shut for a year because they had fully developed their vision during their critical period. Later experiments in monkeys found similar results consistent with the strong critical period.