Age-related Changes In The Brain's White Matter Affect Cognitive Function In Old Age

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."