Exceptional cognitive abilities of some older adults can slip through the cracks unnoticed, as society tends to focus its attention on those who experience major brain-functioning deterioration, and away from those few who are able to retain most of their cognitive skill in old age.
Roberto Cabeza, assistant professor of psychological and brain sciences, has found that aging can cause some people to use multiple areas of their brains--for example, using both sides of the prefrontal cortex--for tasks that they, when they were younger, might have accomplished with just one side of the brain.
Since 1995, Cabeza has been working on a study that analyzes how many older adults are able to recruit the use of both sides of the brain to carry out cognitive activities. As a part of the aging process, older adults develop "fragile bones, their joints do not work as well and they suffer from high cholesterol," Cabeza said. "The brain is an organ of the body. It's affected by aging too."
As adults age, they begin to lose some natural brain functions--specifically, those cognitive functions, such as memory, associated with the prefrontal cortex.
"Certain [brain] functions are lateralized in young adults," Cabeza said, meaning that certain actions are dedicated to one area or side of the brain. For instance, in performing tasks that require the use of memory, brain scans show that most young adults show almost all stimulation occurring in the left prefrontal cortex of their brain. "Older adults show more bilateral activities," Cabeza said.
Cabeza cited two theories that attempt to pinpoint how adults acquire the ability to engage their brains in bilateral activity. One theory is the dedifferentiation theory, which presumes that the phenomenon occurs because of the loss of the ability to use specialized neural mechanisms. If this theory were true, an individual's genes would be regulating the change, Cabeza said.
The compensation theory states that the loss in asymmetry occurs through a psychological mechanism. Under this theory, the phenomenon reflects a change in the way the brains of some older adults perform cognitive tasks.
"This change occurs through a training of the brain," Cabeza said.
In selecting a proper research group for the study, Cabeza and his research partners tested a large group of older adults in their ability to perform specific memory tasks. From the initial research pool, Cabeza's team selected a group of high-performing older adults and a group of low-performing older adults.
After the two test groups were organized, Cabeza administered cognitive tests to each of the individuals in both groups while scanning their brains using positron-emission tomography.
"The high-performing group showed bilateral activities," Cabeza said. "This shows that the change is compensatory."
As adults age and slowly lose proper functioning of their brains, many are able to recruit the usage of both sides of their prefrontal cortex in performing cognitive functions, to compensate for the age-related loss of ability in each individual side of the brain. The lower performance of the other group could be attributed, at least in part, to the individual's incapacity to "functionally compensate" for the loss of ability in the brain.
A possible follow-up study might look at whether the bilateral activity that Cabeza is researching is more prevalent in women than in men, said Erich Jarvis, assistant professor of neurobiology. "Women tend to use both left and right sides of their brain more equally whereas men tend to use either the right or left sides more," Jarvis said.
David Madden, professor of psychiatry and behavioral sciences, whose studies compare healthy older adults to healthy younger adults, said that a future application of this research could be to extend the study beyond cognitive tasks to see how aging affects the brain's ability to process various perceptions through, for example, sight.
Get The Chronicle straight to your inbox
Signup for our weekly newsletter. Cancel at any time.