Nintendo's Brain Age for the DS has sold four million copies worldwide, exhibiting the widespread appeal of a well-executed "non-game."

So far, 600,000 units have sold in the Americas, 3 million in Japan and 500,000 in Europe, according to Nintendo. The company describes the game as the "cornerstone" for its pick-up-and-play Touch Generations brand of games.

Another smart title in the Touch Generations catalog is Big Brain Academy, which consistently appears in the top 10 DS sellers on Amazon.com's sales charts and has sold over 250,000 copies since its June 5 US launch. Nintendo launched Touch Generations in late May, a brand which also includes titles such as Magnetica and Sudoku Gridmaster.

The success of games like Brain Age bodes well for Nintendo's Wii strategy. The company's upcoming console will cater to the same gamers who are attracted to pick-up-and-play games.

Nintendo of America VP of marketing Perrin Kaplan told BusinessWeek in June, "One of our goals was to target people entering the game world for the first time. It's absolutely about tapping into emerging markets."