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. 

Everyone also got an electroencephalogram (EEG) to measure brain activity. Then, everyone was sent home to practice a computer task for a month. One group used one leading brain exercise while the second group used the other. The third group practiced on a control task.The training programmes compared are not the commercial products available sold to consumers, but tools scientists rely on to test the brain's working memory.

Everyone trained five days a week for 30 minutes, then returned to the lab for another round of tests to see if anything about their brain or cognitive abilities had changed.The researchers found that the group that practiced the "dual n-back" exercise showed a 30 per cent improvement in their working memory. That was nearly double the gains made by the group working with the other common task, known as "complex span". The dual n-back group saw squares flashing on a grid while hearing letters. 

They had to remember if the square they just saw and the letter they heard were both the same as one round back. As the test got harder, they had to recall squares and letters two, three and four rounds back. The other test, called "complex span," also involves remembering items in a sequence, but they do not need to continually update the items in their mind."The findings suggest that this particular task is changing something about the brain," said study co-author Susan Courtney, Professor at Johns Hopkins University.