You know that mental challenges are what keep your brain in trim, but even the toughest brain-teaser can start to seem like old hat. What do you do when you’re the office sudoku champion, or you whip through Friday’s and Saturday’s puzzles without setting down your pen ?(!) As cited in Sunday’s New York Times (March 21, 2007), you can take on one of Maki Kaji’s new offerings. He runs the Japanese company called Nikoli, marketing a vast array of puzzling offerings. The company doesn’t invent puzzles, but instead serves as a testing ground for thousands of ideas submitted by Japanese puzzle makers. Maki Kaji says he has at least 250 more puzzles, most known only in Japan, ready to go.