WASHINGTON (Reuters) - The secret to wisdom in old age may be as simple as keeping stimulated and interested in life, researchers said. They said that aging mice who were kept in a stimulating environment - with tunnels, toys and an exercise wheel - grew more new brain cells than bored mice. Fred Gage and colleagues at the Salk Institute in La Jolla, California, were working with "senior citizen" mice that were 18 months old. Half lived in "standard" cages with just food and water supplied, while half were put in a large cage with tunnels, toys and a little wheel to run on. The fun ran out for the aged mice, who were killed after 68 days and their brains examined. Those in the "enriched" cage had three times as many new cells in the hippocampus, a part of the brain important to learning and memory, the researchers reported in the Journal of Neuroscience. "The benefit of the enriched environment appears to be in fostering the survival of new brain cells," Dr. Gerd Kempermann, who worked on the study, said in a statement.