As every athlete knows, the only way to stay in shape is regular exercise. If unused, the strongest, firmest muscles will begin to turn flabby or even atrophy. The brain is not a muscle, but some of the same logic applies. The brain stores information by adjusting connections between individual brain cells, called neurons. These connections are always in flux: those that are in constant use grow stronger, while those that are seldom activated tend to weaken and fade away. So, "brain exercise" strengthens memory, just as physical exercise strengthens muscles.

In the lab, rats placed in "enriched" environments-given plenty of toys to play with and companions to socialize with-show more brain growth and are smarter than rats who lead more boring lives. In humans, people who get plenty of brain exercise have better memories and are less likely to develop age-related memory disorders such as Alzheimer's disease.

How can you exercise your brain? By doing anything that pushes your brain to work hard. Play complicated games (bridge, Scrabble, chess) for a good mental workout. Do a crossword puzzle. Read a mystery novel and try to unmask the killer before the detective does. T

ake a class at your local community college and learn to speak another language, or play a musical instrument, or dance. Travel is another great way to have new experiences. The challenge of organizing a trip and finding your way around a strange place takes a lot of brain work. The destination doesn't matter: going to Italy is wonderful, but a local sightseeing trip can also pay off in terms of new experiences.

Even having a stimulating conversation with a friend can exercise your brain: discuss politics or child-rearing techniques or the designated hitter rule, but challenge each other's ideas so you're both forced to think about what you're saying.

Anything that shakes up the day's routine can provide mental exercise. Having a steady stream of new experiences will help keep your brain healthy-and is also a key component of a fulfilling and enjoyable lifestyle.

Further Reading:

Rats:

• "Neural consequences of environmental enrichment," H. van Praag and others, Nature Reviews Neuroscience, December 2000, vol 1., pp. 191-198.

Humans:

• "Participation in cognitively stimulating activities and risk of incident Alzheimer disease", R. Wilson and others, Journal of the American Medical Association, February 2002, vol. 287, no. 6, pp. 742-748,