The passage of time produces changes in both the behavior and the brains of organisms. A number of useful animal models of learning and memory in normal aging have expanded the knowledge base and extended the prospects for ameliorating learning and memory deficits. Completion of the mapping of the human and mouse genome and the development of transgenic mouse models in the 1990s have accelerated insights about mechanisms of learning, memory, and aging. Since the mid-1990s, mouse models of neuropathology in Alzheimer's disease have become available for behavioral testing. Two features of animal models make them invaluable: First, the life spans of most animals are considerably shorter than the human life span, compressing the time required to observe processes of aging. Second, invasive or high-risk observations and experimental manipulations are feasible with animals but not with humans.

Aging is...