My latest column in the WSJ is now online. It's about a forthcoming PNAS paper on the n-back test and fluid intelligence:

Can we make ourselves smarter? In recent decades, scientists have accumulated increasing evidence that our intelligence, at least as measured by the IQ test, is sharply constrained by genetics. Although estimates vary, most studies place the heritability of intelligence at somewhere between 50% and 80%. It's an uncomfortable fact, but not all brains are created equal.

Which is why there's so much buzz about a forthcoming study that complicates this assumption. Researchers at the University of Michigan found that it's possible to boost a core feature of human intelligence through a simple mental training exercise.

In fact, when several dozen elementary- and middle-school kids from the Detroit area used this exercise for 15 minutes a day, many showed significant gains on a widely used intelligence test. Most impressive, perhaps, is that these gains persisted for three months, even though the children had stopped training.

Scientists typically describe intelligence as consisting of two distinct components: fluid intelligence and crystallized intelligence. Fluid intelligence refers to the general ability to solve new problems and recognize unfamiliar patterns. Crystallized intelligence, by contrast, consists of particular kinds of knowledge. When children learn to count, for instance, they show gains on crystallized intelligence, even as their fluid intelligence remains constant. Scientists have typically regarded fluid intelligence as the aspect of our thinking that is most determined by genetics, since it can't be easily taught.

And yet these schoolchildren showed gains in fluid intelligence roughly equal to five IQ points after one month of training. The IQs of 68.2% of the populace fall within a 30-point range, so this is a significant change. These kids weren't learning facts they would soon forget. They were learning how to think better.

These improvements were triggered by a mental exercise known as the n-back task. The exercise is not fun, even when translated into videogame format. It begins with the presentation of a visual cue. For the kids in the experiment, the cue was the precise location of a cartoon character. In the next round, the cue is altered—the cartoon character has moved to a new location. The job of the child is to press the space bar whenever the character returns to a spot where it has previously been, and to ignore the other irrelevant locations. As the children advance in the task, these locations move further back in time, forcing them to sort through an increasing amount of information.

How does this tedious exercise boost intelligence? The crucial change concerned the nature of the children's attention. After repeatedly playing the n-back game, the young subjects were better able to focus on the necessary facts. As a result, they squandered less short-term memory on irrelevant details, such as cartoon locations they didn't need to recall. The children "got better at separating the wheat from the chaff across a variety of different tasks," says John Jonides, a senior author on the paper.

There are two important caveats to this research. The first is that not every kid showed such dramatic improvements after training. Initial evidence suggests that children who failed to increase their fluid intelligence found the exercise too difficult or boring and thus didn't fully engage with the training.

The second caveat concerns the relevance of the mental improvement. Scott Barry Kaufman, a cognitive scientist at New York University who was not involved in the research, believes that while this study has "incredibly important potential implications," it's unclear if the children's performance changed on anything besides an abstract intelligence test.

Still, this research promises to change longstanding beliefs about the nature of intelligence. Our IQ scores may be bounded by our genes, but it looks as if it's possible to significantly increase measured intelligence after only a few hours of training. "Intelligence is a lot like height," Prof. Jonides says. "We know that how tall you are is largely determined by the height of your parents. But we also know that better nutrition can make everyone a lot taller. Perhaps the n-back task is just an ideal form of mental nutrition."

Although we can't choose the brain we've been given, we can choose what that brain is paying attention to. All it takes is a little practice.