It's rare that a video game comes along that's so original that it doesn't fit into any pre-existing categories.

Take Nintendo's "Brain Age: Train Your Brain in Minutes a Day." Is it an educational game? A puzzle game? Or (heaven help us) "edutainment"?

When "Brain Age" came out last year for the Nintendo DS, many critics didn't know what to make of it. It's essentially a fast-paced collection of arithmetic, logic and observation problems; some players questioned whether you could even call it a game.

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But more than a million people bought it (it was 2006's seventh-best-selling game). It seems to have found an audience, outside the usual gaming crowd, of older players enticed by its promise that it could help keep their minds sharp.

A follow-up, "Big Brain Academy," also did well — but Nintendo has since stayed away from the genre it created, with no new "brain training" games yet scheduled for the United States.

Naturally, other publishers are filling the void. Forget about whether video games can actually make you smarter; the real question is whether you'll feel like a dummy for buying a "Brain Age" rip off.

—"Mind Quiz" (Ubisoft, for the PlayStation Portable, $19.99): PSP owners who missed out on "Brain Age" can get a close facsimile with "Mind Quiz."

Like its predecessor, "Mind Quiz" is "supervised" by a prominent Japanese brain scientist; likewise, each session is a rapid-fire bombardment of visual and mathematical brainteasers.

You may be asked to solve a multiplication problem, memorize shapes or count pictures — nothing an average third-grader couldn't do, but you're graded on speed and accuracy.

With 49 different exercises, there's enough here to keep your gray matter humming for a while. In a blatant nod to the Nintendo game, "Mind Quiz" even tells you what your "brain age" is (the lower the better).

The biggest drawback is a hardware issue: Since the PSP doesn't have the DS's nifty touch screen, your input is limited to the four buttons on the face of the machine, turning each question into multiple choice.

That makes "Mind Quiz" a little bit easier, but it's still a decent "Brain Age" clone for PSP die-hards.

Two stars out of four.

—"Brain Boost: Beta Wave" and "Brain Boost: Gamma Wave" (Majesco, for the Nintendo DS, $19.99 each): The "Brain Boost" manuals credit yet another Japanese brain expert, but the games look like something he could have sketched out in just an afternoon. Each cartridge consists of five — count `em, five — exercises.

"Beta Wave" is meant to improve your concentration, asking you to add numbers, match pictures or recognize shapes. "Gamma Wave" focuses on memory skills, asking you to memorize numbers, colors or faces.

In either case, you'll run out of things to do in less than half an hour, and neither game keeps track of your day-to-day performance like "Brain Age" and "Mind Quiz" do.

"Beta Wave" and "Gamma Wave" could have easily been combined into one package, but they still wouldn't offer as much fun as the Nintendo original.

No stars.

—"Online Chess Kingdoms" (Konami, for the PlayStation Portable, $29.99): Perhaps we should just go back to a game regarded by many as a superb tool for sharpening the mind. "Online Chess Kingdoms" lets you play the classic game against other PSP owners (if you can find them online) or against a fairly competent computer.

That's probably enough for any chess-loving PSP user ("Kingdoms" is the only such game for the system), and the extras here are really just distractions.

There's a ridiculous "battle chess" mode in which you move your pieces as quickly as possible without taking turns; it's too chaotic to be interesting. And there's a tedious "campaign" mode in which individual chess games become skirmishes in a larger battle between two armies.

"Kingdoms" offers a variety of sci-fi- and fantasy-inspired chess sets, but sometimes it's hard to tell one piece from another; purists will want to stick with the classic game and more traditional pieces.

Two stars.