Researchers have found that practicing what is known as a "dual n-back" exercise can lead to improvement in working memory, which is what people rely on to temporarily hold details in their mind like phone numbers and directions.

The "dual n-back" is a memory sequence test in which people must remember a constantly updating sequence of visual and auditory stimuli.

"People say cognitive training either works or doesn't work. We showed that it matters what kind of training you're doing," said lead author Kara Blacker who was with Johns Hopkins University in Baltimore at the time of the research.

"This one task seems to show the most consistent results and the most impact on performance and should be the one we focus on if we're interested in improving cognition through training," said Blacker, now a researcher at the Henry M. Jackson Foundation for Advancement of Military Medicine Inc in Maryland.

The researchers decided to compare directly the leading types of exercises and measure people's brain activity before and after training.

First, the team assembled three groups of participants, all young adults. Everyone took an initial battery of cognitive tests to determine baseline working memory, attention and intelligence.