Brain exercise has been a hot topic lately. Baby Boomers and test-prepping school kids alike want to challenge themselves. In fact, a recent Time magazine article cited Brain Age in its exploration of the trend of people looking for ways to exercise their brains.

But Baby Boomers picking up a video game system? It's not as far-fetched as you might think. Three separate titles in the brain-training series are currently a huge craze in Japan. Each of them has achieved sales of more than 1 million units, with the most recent title hitting that milestone in less than a month. The craze has been fueled largely by older players, many of whom had never played a video game system before.

Brain Age (known as Brain Training in Japan) was inspired by the work of Professor Ryuta Kawashima, a prominent Japanese neuroscientist. His studies evaluated the effect of performing reading and mathematic exercises to help stimulate the brain.

Brain Age presents players with a series of fun mental brain-training challenges that incorporate word memorization, counting and reading. It even includes sudoku number puzzles, which have become extremely popular features in newspapers around the country. The distinctive touch screen of Nintendo DS lets users write their responses, just as though they were using a PDA. Players even turn the Nintendo DS sideways to make it feel more familiar, like a book. The more often users challenge themselves, the better they become at the tasks and the lower their estimated DS "brain age."

Nintendo's brain-training series of games represent a cornerstone of Nintendo's aim to expand the world of video games to new audiences. The second title in the series, Big Brain Academy (known as Brain Flex in Japan) offers players 15 fun activities that test their brain powers in areas like logic, memory, math and analysis. Up to eight people can play with a single game card, and each activity takes less than a minute to complete.

Brain Age: Train Your Brain in Minutes a Day is rated E for Everyone and launches on April 17. Big Brain Academy is Rated E for Everyone and launches May 30.