Memory capacity may be linked to filtering out irrelevant information

People who are good at remembering things, even with distractions, have more activity in the basal ganglia on brain scans, the Swedish team found.

The work in Nature Neuroscience could help explain why some people are better at remembering things than others.

Clinically, it could also aid the understanding of attention deficit hyperactivity disorder (ADHD).

The ability to hold information in the mind so that it is immediately accessible is known as working memory.

We use working memory all of the time - for example, when doing a simple maths calculation in our head or recalling a telephone number.

There will be many brain regions that filter irrelevant information, so it is too early to tell if these findings will have a bearing on conditions such as ADHD

John Duncan

Medical Research Council scientist

Its capacity is limited and seems to vary from person to person.

These variations are not just due to having a larger or smaller memory store, but also due to differences in how effectively irrelevant items are kept out of memory, the Karolinksa Institute researchers believe.

Distracters

Dr Torkel Klingberg and colleague Fiona McNab used a special brain scan called functional magnetic resonance imaging (fMRI) to track what was happening in the brains of 25 healthy volunteers.

The volunteers were asked to perform a computer-based task that required them to respond to target visual images, with or without distractions.

A noise informed subjects when an upcoming visual display would contain irrelevant distracters along with the targets.

When this cue occurred, neural activity increased in the basal ganglia and the prefrontal cortex before the visual display appeared, suggesting the brain was preparing to "filter out" the upcoming distracters.

Also, greater activity in a specific part of the basal ganglia - the globus pallidus - correlated with less unnecessary storage in another part of the brain, the posterior parietal cortex, which is sensitive to the amount of information held in memory.

The team is currently investigating methods of improving attention and working memory in children with ADHD and monitoring any changes with fMRI.

Medical Research Council scientist John Duncan said: "This is very interesting work and gives a window on important parts of the brain.

"The basal ganglia are very strong candidates for involvement in brain disorders where people have difficulty with attentional control.

"But there will be many brain regions that filter irrelevant information, so it is too early to tell if these findings will have a bearing on conditions such as ADHD."