Inability to filter distractions can result in short-term memory 'overload,' new studies indicate.

Older patients often report difficulty tuning out distractions while engaging in such activities as driving, socializing and reading. The UC Berkeley team, led by Dr. Adam Gazzaley, used magnetic resonance imaging (MRI) to pinpoint the processes in the brain that are responsible for this circumstance.

Memory failure owes more to interference from irrelevant information than to an inability to focus on relevant information, results indicate.

Gazzaley and his colleagues compared memory capabilities of young adults aged 19 to 30 with older adults aged 60 to 77. Researchers used MRI to first pinpoint the areas in the subjects' brains that are activated when observing images of both faces and natural scenes (they differ slightly in each individual).

Ability to Focus Is Not Enough

Participants were then given a simple memory test wherein they were shown a sequence of four images, two of them faces and two natural scenes. They were instructed to remember either faces, in which case the scenes were irrelevant information; or scenes, in which case the faces were irrelevant. Afterward, they were asked whether a particular face or scene had appeared among the four images.

When asked to remember faces, young adults showed enhanced activity in the brain area dealing with faces and decreased activity in the area dealing with scenes. Similarly, when asked to remember scenes, they showed enhanced activity in the scene area of the brain and suppressed activity in the area dealing with faces.

Older adults also showed enhanced activity in areas of the brain that correlates to the images they were asked to remember. However, they exhibited little or no suppression of the images that were irrelevant.

While young subjects were easily able to suppress brain activity in areas that process information irrelevant to the memory task, older adults on average were unable to suppress such distracting information. Both groups were equally able to enhance brain activity in the areas dealing with information relevant to the task.

Unsuppressed Distractions Overload System

"These results reveal that efficiently focusing on relevant information is not enough to ensure successful memory," Gazzaley suggests. "It is also necessary to filter distractions. Otherwise, our capacity-limited short-term memory system will be overloaded."

Interestingly, six of the sixteen older adults had well-functioning short-term memories and no problems ignoring irrelevant information. Gazzaley hopes to find out what makes these people different from the average aging adult.

"Aging is not a disease, but I think there likely is a problem that could be fixed with drugs," Gazzaley says. Drugs that target the inability to suppress distraction may prove to be effective in treating age-related cognitive problems, as well as a wide range of memory-related problems, he suggests.

Probing the Frontal Lobe

Gazzaley's technique of using MRI to probe the brain's focusing and suppressing ability will make it possible to advance research on the popular theory that problems of aging are due to a decline in the brain's frontal lobe, according to study co-author Dr. Mark D'Esposito.

"If you look at the frontal lobes over time, that is the area where there is more decline than any other part of the brain," D'Esposito notes.

Gazzaley and D'Esposito plan to conduct studies on patients with frontal lobe damage to see if they have problems with focusing or suppressing. They also plan to look at people with attention deficit disorder, addiction problems, and mild cognitive impairment in search of evidence that these problems are also due to dysfunction of the frontal lobe.

"If aging is a frontal lobe dysfunction, it is a mild form of it," D'Esposito suggests. Studies on aging and frontal lobe dysfunction could lead to more effective treatments for patients with more severe forms of frontal lobe damage like traumatic brain injury, strokes and dementia, he adds.

Results of the study will be published in the September 11 issue of the online journal Nature Neuroscience.