Brain researchers for the first time claim to have found a method for improving the general problem-solving ability scientists call fluid intelligence, otherwise known as "smarts."

Fluid intelligence was previously thought to be genetically hard-wired, but the finding suggests that with about 25 minutes of rigorous mental training a day, healthy adults could improve their mental capacities.

The method, if commercialized, could be a boon to the growing, multimillion-dollar market for "brain fitness" software like Nintendo's Brain Age.

"The most important point of our work is that we can show that it is possible to improve fluid intelligence," said Martin Buschkuehl, a psychology researcher based at the University of Bern, Switzerland. "It was assumed that fluid intelligence was immutable."

Fluid intelligence measures how people adapt to new situations and solve problems they've never seen before. Fluid intelligence differs from crystallized intelligence, which takes into account skills and knowledge that have been acquired – like vocabulary, grammar and math.

It's not hard, for example, for students to improve their IQ scores by taking lots of IQ tests.

Trouble is, learning how to take IQ tests doesn't improve the underlying smarts. The students just get better at taking tests. In practical terms, people can get better at taking tests, but in daily life, don’t have a blazingly quick new brain.

And that's where Buschkuehl's research, which appears today in the journal Proceedings of the National Academy of Sciences, claims to be groundbreaking.

In a limited trial, he and his team were able to make 34 test subjects significantly better at answering IQ test questions after training them on a completely separate memory task.

David Geary, a professor at the University of Missouri and author of The Origin of Mind, who was not involved with the study, said training in one test generally doesn’t generate gains on a different test.

"Transfer is tough to get," Geary said. "Training in task A doesn’t typically improve performance on task B."

But in this case, subjects trained on a complex version of the so-called "n-back task" – a difficult visual/auditory memory test – improved their scores on a set of IQ questions drawn from a German intelligence measure called the Bochumer Matrizen-Test. (The Bochumer Matrizen-Test is a harder version of the well-known Ravens Progressive Matrices).

Initially, the test subjects scored an average of 10 questions correctly on the IQ test.

But after the group trained on the n-back task for 25 minutes a day for 19 days, they averaged 14.7 correct answers, an increase of more than 40 percent. (A control group that was not trained showed only a very slight performance increase.)

Buschkuehl's team postulates that the n-back task improves working memory – how many pieces of information subjects can keep in their head – as well as the ability to control the brain's attention. Fluid intelligence tests require those types of thinking, and the training improved performance in these underlying skills.

"These are intriguing results," Geary said. However, Geary noted that to claim actual increases in fluid intelligence, the subjects would have to show the performance gains over a long-term period – or even permanently.

The Michigan researchers are now engaged in studying the long-term effects of training. They are also working to increase the amount of training that users undergo. In the experiment reported in PNAS, the researchers did not find the upper-limit for improvement, suggesting that more training could yield even better mental performance gains.

"The improvement seems to be dosage dependent," Buschkuehl said. "We saw a linear increase in performance with increase in training time."

In the simplest version of the n-back task, a sequence of images is presented every few seconds and subjects are asked to match a picture to an identical one that came previously, say two pictures before it. (For example, in the picture above, the blue square should be in the same location.)

Buschkuehl's subjects, however, also heard a second stream of letters and had to match the sounds at the same time as they matched the visuals. This makes the task very challenging. And as the subjects got better, the gap between matching pictures and letters got bigger, making the task progressively more difficult.

The team has developed a new n-back computer program called Brain Twister, which they have translated into English, but is not available online.

They do not plan to commercialize the software, but with mental gyms like Vibrant Brains in San Francisco springing up, and brain training software companies like Posit Science drawing big-name investors, you can bet you'll be seeing the n-back task on sale sooner rather than later.

In fact, revenue from "brain-fitness software" reached $225 million in 2007, according to SharpBrains, a market-research firm.

In the meantime, a very simplified, DIY version of the n-back is described here.

Neurobehavioral Sciences also offers a 45-day free trial of their neuroscience stimuli program presentation, which is primarily a research tool, and only available for the PC.