Age-related changes in the brain's white matter affect cognitive
function in old age
March. 25, 2003
Scottish researchers studied adults whose cognitive abilities were
first tested in 1932, when they were 11
Age-related changes in the brain -- the appearance, starting around age
60, of "white-matter lesions" among the brain's message-carrying axons --
significantly affect cognitive function in old age. White-matter lesions are
small bright patches that show up on magnetic resonance imaging (MRI) of the
brain. What's more, hypertension may account for some of this cognitive
impact. A full report on these relationships appears in the March issue of
Psychology and Aging, which is published by the American Psychological
Association (APA).
Psychologists want to find the factors that contribute to individual
differences in cognitive functioning among the elderly, because, says lead
researcher Ian Deary, Ph.D., "People who retain their cognitive function in
old age tend to have higher quality of life and live longer." However,
researchers have been stymied by the lack of data on the childhood cognitive
performance of elderly individuals. Without that data, it is hard to tell
whether individual differences are due to aging or existed all along.
Luckily, Deary, from the University of Edinburgh, and his colleagues at the
University of Aberdeen, discovered that on June 1, 1932, Scotland gave its
11-year-olds a validated cognitive test. With its results, the authors
gained a measure of early-life cognitive ability for people who were in
their late 70s at the time of the study.
Deary and his co-authors used local health registers to track down
healthy living men and women who took the Scottish Mental Survey of 1932. Of
the 427 possible matches, they contacted 327 people chosen at random; 83 of
those people took part in a brain imaging study.
Testing took place in 1999, when most participants were 78 years old.
Participants took four different cognitive tests, examining nonverbal
reasoning, memory and learning, processing speed, and executive function.
They also underwent magnetic resonance imaging (MRI) of their brains to
allow researchers to assess the extent of white-matter lesions, which are
like little scars in the brain.
The amount of brain white-matter abnormalities made a significant
contribution to general cognitive ability differences in old age,
independent of prior ability. In other words, if "Mary" tested better than
"Billy" at age 11, they didn't necessarily test the same way at age 78. An
elderly Mary might still have tested better, but the gap could have widened,
narrowed or reversed --- and the differences in their white-matter lesions
would matter more than differences in their earlier ability. In old age, the
amount of white-matter lesions contributed 14.4 percent of the variance in
cognitive scores; early IQ scores contributed 13.7 percent of the variance.
What's more, these two predictors of cognitive performance in old age
were independent; they didn't consistently affect scores in the same way.
That is, after taking into account people's mental ability in youth, these
researchers establish a factor that contributes significantly to people's
cognitive function in healthy old age.
Although white-matter lesions are viewed as a normal part of aging, and
are found in people with no dementia or other neurocognitive disorders, they
are linked with other health problems. In this study, hypertension accounted
for a small but significant amount of variance both in white-matter lesion
scores and in general cognitive scores in old age. This finding builds on
other recent evidence that white-matter abnormalities may be related to
circulatory problems (including hypertension, diabetes, heart disease and
cardiovascular risk factors).
Given the role played by white-matter abnormalities in cognitive
performance, "Avoiding risk factors for [them] or preventing their
accumulation may ameliorate age-related cognitive decrements," say the
authors. "The understanding of the functional neurobiology of brain aging
will be enhanced by the discovery of interactions among etiological
factors."
In a side note, Deary and his colleagues observe that, "the search for
the causes of intelligence differences in youth is relevant to research on
aging because much variance from youth persists into old age."
American Psychological Association
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