Aging lowers activity in brain's language areas; performance unaffected

November 06, 2002

Functional magnetic resonance imaging (fMRI) studies of the brain show that despite the decrease in brain activity that naturally occurs in aging, particularly in the language areas of the left frontal lobe, some types of language processing may be performed more efficiently in older individuals.

Results of these experiments, performed by Darren Gitelman, M.D., and colleagues at the Cognitive Neurology and Alzheimer's Disease Center at Northwestern University, stand in contrast to performance and brain imaging findings in other areas of brain function, such as memory, attention and response speed, where older persons show decreased performance and efficiency when compared with younger populations.

The findings, which Gitelman and his co-investigators presented at today's Society for Neuroscience meeting in Orlando, Fla., are consistent with theories that suggest that some brain functions may be preserved with age.

"These results show that despite equivalent performance, the brain is not a static organ and may accomplish the same task in different ways as a function of a person's age," said Gitelman, an associate professor of neurology at The Feinberg School of Medicine at Northwestern University.

The results also are important because instead of comparing brain activity and performance in older vs. younger groups of adults, Gitelman and co-researchers used participants who ranged from 23 to 78 years old.

"We demonstrated that brain activity changes occur slowly with age and not as a sudden change occurring in latter decades," Gitelman said.

In the study, 50 participants who were healthy, right-handed and had no evidence of a decline in thinking abilities performed a pronunciation task that involved reading pairs of words and deciding whether the word pair was a homonym, e.g., "reign" and "rain." They also performed a word meaning task that involved reading pairs of words and deciding whether each word pair was a synonym, e.g., "boat" and "ship."

Brain activity during these tasks was compared with brain activity during a baseline task, which was measured while participants matched consonant letter strings, e.g., "zqqpf" and "zqqpf." The comparison between each language task and the control task allowed the demonstration of brain regions more specifically devoted to language as opposed to low-level functions such as vision and generating a response, Gitelman explained.

Participant performance was recorded during imaging, and brain activity was assessed by measuring signals while the individual performed the tasks in a 1.5 Tesla magnetic resonance scanner. The signals, which are a measure of changes in blood oxygenation known as BOLD imaging, have been shown to correlate with brain blood flow and indirectly with brain activity.

The imaging showed that increasing age was associated with reduced brain activity, mainly in the language areas of the left front lobe but also in the left parietal cortex and high-level visual regions on both sides of the brain. The parietal cortex participates in word pronunciation and the decoding of meaning (among many other functions). The visual areas are concerned with processing written material. Increased brain activity with age was seen in an area of the brain known as the posterior cingulate cortex, which is concerned with attentional behaviors.

These findings demonstrate that aging changes language-related brain activations both within and outside the traditional language network, Gitelman said.

"The predominant decreases in front lobe activity for both tasks could reflect a greater processing efficiency for the older subjects given their equivalent performance," he said.
Gitelman's co-investigators on this project were M.-Marsel Mesulam, M.D., Ruth and Evelyn Dunbar Professor of Psychiatry and Behavioral Sciences, professor of neurology and director of Cognitive Neurology and Alzheimer's Disease Center; Sreepadma Sonty [please cite first name and academic title]; Anna C. Nobre, adjunct associate professor of neurology; and Todd Parrish, associate professor of radiology at the Feinberg School and biomedical engineering, McCormick School of Engineering and Applied Science.

This study was supported by a grant from the National Institute of Aging.

Northwestern University

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