As a baby boomer, it's like a treadmill for my mind."

It seems more than just a few people want to train their brains, as Nintendo's Brain Age has sold more than 4 million copies of the game worldwide. They've sold 3 million in Japan alone, and then 600,000 units in America and 500,000 copies in Europe.

"Brain Age is so easy to pick up and play, regardless of your experience level," says George Harrison, Nintendo of America's senior vice president of marketing and corporate communications, whose "Brain Age" has improved to age 20 (the best score you can achieve). "You can play it for 10 minutes or an hour and keep yourself feeling sharp. As a baby boomer, it's like a treadmill for my mind."

It begs the question, though, looking at the breakdown of sales of Brain Age in the various countries: Why is it so popular in Japan, and conversely, why haven't Americans or Europeans adopted the game with the same level of enthusiasm? Dick Stroud