Most gamers know the video game scene in Japan is different than the one in the U.S. But wrap your head around this: The hottest video game in Japan right now is a Nintendo-made IQ test.

A Pacific Ocean away, in a land where first-person shooters don't sell and horse-racing and Gundam games do, "Brain Training for Adults" for the Nintendo DS is the hottest game on the market. That's not all that's different. The PSP is in a slump, and few people buy Xboxes anymore. Has the gaming world gone mad?

The overall context for gaming in Japan these days -- and in a way the impetus for Nintendo's IQ game -- is that, unlike in the U.S., it's not as popular as it used to be.

Pity a gamer like Jonathan Lumb, 29, a Web developer who hails from Leeds, England, but now lives in Tokyo. "I've been here for five years, and I actually came here because of my love of games," he said. "I'm sad to say that I have seen a marked decline in the industry since coming here."

The Japanese gaming industry is still a big deal, but it's just not booming the way it did in the heyday of the "Mario" titles or even "Final Fantasy." "In terms of absolute industry dollar signs, they have been in decline for the last four years," said Reggie Fils-Aime, executive vice president of sales and marketing at Nintendo of America.

Not everyone has agreed that there is a Japanese gaming crisis. Sony executives pointed to strong PS2 sales. But, problem or not, Nintendo offered a solution: unconventional game titles.

First this year came "Electroplankton." It was less of a game than a collection of interactive sound and light shows, culled from the mind of Japanese artist Toshio Iwai. In one section, players fired digital fish at bright green leaves, adjusting the leaves' position to affect the notes that sounded with each collision. Attractive and odd, the game is still being considered for a U.S. release, according to Fils-Aime. But in Japan it flopped.

Next came April's "Nintendogs," a virtual pet for the 21st century, featuring realistic-looking puppies that players could pet with the DS touch screen and train with vocal commands shouted into the system's microphone. "Nintendogs" sold more than 650,000 copies in its first two months, according to Nintendo, and is confirmed for a U.S. release in August.

And then there was "Brain Training for Adults," which has sold more than 200,000 copies in the past six weeks, a striking number considering its unusual design and pedigree. "Brain Training" is played on the Nintendo DS. Players hold the two-screened handheld sideways, using one side to write answers while the other side drills the player on math, logic and trivia. Play the game each day and it will track accuracy and response time in order to chart changes in the user's mental performance.

It may sound weird, but it's got an even weirder back story. "Brain Training" is based on a best-selling series of Japanese books devoted to strengthening one's brain with the use of daily math drills. The author, Ryuta Kawashima, made international headlines five years ago after conducting a study that suggested playing video games exercised the brain less than doing math. Five years later, the game critic became the face of Nintendo's IQ brain-training game.

"On a personal level, I've been impressed by all the new nontraditional titles that Nintendo has released recently," Lumb said. "But more important than that is that I've actually been able to involve my wife in my hobby. She loves the 'Brain Training' game and we played it religiously every day ... comparing scores and talking about it."

The influx and success of these unconventional games is one of the big stories in Japanese gaming this year and, if a title such as "Nintendogs" makes a mark, may well have an effect on what games are sold here. But things aren't all different in Japan, and in some ways the two most game-crazy nations in the world have become more similar. For example, "Grand Theft Auto" has belatedly taken a small foothold in the market -- and inspired an American-style round of concern over violent video games in the process.

Another common factor is that the same video game machine still dominates in both nations. "The general perception is that the PS2 is for adults and the 'cool' people, while the GameCube is more for teenagers and younger kids," said John Ricciardi, 30, a part-time games journalist who lives in Tokyo and works for a company that translates games from Japanese to English.

But then there is the fate of that other console, the one that plays "Halo." "Xboxes are there for the people who can't stand Sony products in their house, basically," Lumb said.

"You won't find much dust in a [Japanese] video game store," said Richard Doherty, who watches the gaming and electronics industry as director of research at Envisioneering, an American firm. "But you do find dust on Microsoft boxes."

In the last full week of June, the PS2 sold more than 28,000 units, according to Media Create, a firm that tracks Japanese game sales. The GameCube sold about 2,600. The Xbox sold 184. (The DS topped the chart with more than 32,000 sold; PSP had over 20,000; and, in a showing much higher than normal, the Game Boy Advance SP sold more than 21,000.)

The perceived market slump seems to have inspired Nintendo to create a wave of unusual games. The failure of Xbox in Japan has spurred Microsoft to enlist top-flight Japanese developers to commit to making games for the Xbox 360. Top designers formerly from Capcom and the "Final Fantasy" series are already on board, as is Tetsuya Mizuguchi, the designer of the PSP puzzle hit "Lumines."

From adversity come new opportunities for gamers. Will the struggles in Japan reap good games for Americans? Time will tell.