Researchers, however, are more optimistic than ever about the potential of the aging brain, because recent evidence has challenged long-held beliefs by demonstrating that the brain can grow new nerve cells.

The birth of new nerve cells, she said, “has been shown to occur in the adult — not only in adult rats and monkeys, but also in older adult humans.” Most of the areas that show neurogenesis and that have been investigated so far are important for learning and memory, particularly the hippocampus, she added.

So how does one stimulate neurogenesis?

Scientists do not have all the answers, but studies of older people who have maintained their mental acuity provide some clues. They tend to be socially connected, with strong ties to relatives, friends and community. They are often both physically healthy and physically active. And they tend to be engaged in stimulating or intellectually challenging activities.