Recent work, albeit mostly in rats, indicates that learning enhances the survival of new neurons in the adult brain. If you watch TV, earl magazines or surf the Web, you have probably encountered urging you to exercise your mind. It sounds a bit gimmicky, but such programs may have a real basis in neurobiology. Various brain fitness programs encourage people to stay mentally limber by giving their brain a daily workout € doing everything from memorizing lists and solving puzzles to estimating the number of trees in Central Park.

And the more engaging and challenging the problem, the greater the number of neurons that stick around. These neurons are then presumably available to aid in situations that tax the mind.

The findings may be particularly interesting to intellectual couch potatoes whose brains could benefit from a few cerebral sit-ups. More important, though, the results lend some support to the notion that people who are in the duffy stages of Alzheimer € disease or who have other forms of dementia might slow their cog nitive decline by keeping their minds actively engaged.

It seems, then, that a mental workout can buff up the brain, much as physical exercise builds up the body.