Evidence for age-related changes in spatial memory in rodents and humans is presented, along with data that suggest that the hippocampal formation is necessary for normal performance on spatial tasks in both species. An examination of the electrophysiological characteristics of this structure in rats suggests that the changes that occur with age in the hippocampus are selective, but that at least two primary types of alterations contribute to the spatial cognitive impairment seen in these animals. These include a deficit in the ability to maintain synaptic enhancement and a reduction in the accuracy of information processing ability of single hippocampal neurons.