Spatial and temporal sensitivity degradation of primary visual cortical cells in senescent rhesus monkeys.

Human visual function declines with age. Much of this decline is mediated by changes in the central visual pathways. In this study we compared the spatial and temporal sensitivities of striate cortical cells in young and old paralysed macaque monkeys. Extracellular single-unit recordings were employed. Our results show that cortical neurons in old monkeys exhibit lower optimal spatial and temporal frequencies, lower spatial resolution and lower high temporal frequency cut-offs than do cells in young adult monkeys. These changes in old monkeys are accompanied by increased visually evoked responses, increased spontaneous activities and decreased signal-to-noise ratios. The increased excitability of cells in old animals is consistent with an age-related degeneration of intracortical inhibition. The degradation of spatial and temporal function in old striate cortex should contribute to the decline in visual function that accompanies normal aging.