Researchers at the University of California, Berkeley, suggest brains that continue to perform well in old age, against odds that they are slower and less accurate in short-term memory compared to those of younger people, do so by rallying more of the brain to complete mental tasks.
"We think this pattern of increased connectivity between frontal regions and other modules in the brain reflects a more integrated network architecture that is key for successful performance of executive control tasks in aging," said UC Berkeley graduate student Courtney Gallen, who worked with her colleagues on a study published in the August issue of the journal Neurobiology of Aging.
Under the direction of her thesis adviser Mark D' Esposito, a UC Berkeley professor of psychology, the researchers compared 18 adults in their 20s to 38 healthy people age 60 and older.
They found that the older study subjects showed larger changes than younger subjects in the organization of brain networks between a task-free state and performing a task, and that those who did not exhibit this adaptation in brain signaling were less adept in performing tasks.
"Executive control" functions are thought to underlie humans' ability to flexibly change thinking and behaviors and to solve problems.
Using functional magnetic resonance imaging (fMRI) to track communication within specific brain sub-networks - called modules - and connections made across different modules, the researchers also found that the structural integrity of the superior longitudinal fasciculus (SLF), which anatomically connects frontal and posterior brain regions important for short-term memory, was associated with older subjects' likelihood of exhibiting the transition to the more interconnected communication between brain regions that in turn was linked to better performance of tasks.
With focus was on the frontal cortex, which is critical for executive functions, and its connections to other parts of the brain during fMRI scanning, the researchers asked participants to perform four different tasks in two-minute trials, with five trials assigned to each participant for each task.
Images of faces and scenes, each selected from a set of 10, were flashed before the subjects sequentially, with each displayed for six-tenths of a second, followed by a pause of varying length before the next was displayed.
The easiest task required participants to press a button to categorize a displayed image as either a scene or a face, and the most difficult task was to recall both the previous face and previous scene.
Compared to a task-free "resting state," older adults performing tasks of any difficulty recruited additional between-module connections. In contrast, younger adults recruited additional between-module connections only for the most difficult task.
Most previous research in which researchers looked at age-related changes in brain function due to specific cognitive demands focused on activation of individual brain regions rather than taking a network approach, Gallen said in a news release from UC Berkeley.
Earlier studies showed that frontal activity in the brain increases in older adults compared to younger adults during less-demanding cognitive tasks.
"Our new results further support the idea of compensatory recruitment and suggest a large-scale network-level mechanism by which the aging brain reorganizes to support executive control processing," she said.