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November
4, 2002
Aging
Doesn’t Affect Language Processing
CHICAGO
--- 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; 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.
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