As we get older, our cognitive abilities change, improving when we’re younger and declining as we age. Scientists posit a hierarchical structure within which these abilities are organised.

There’s the “lowest” level— measured by specific tests, such as story memory or word memory; the second level, which groups various skills involved in a category of cognitive ability, such as memory, perceptual speed, or reasoning; and finally, the “general,” or G, factor, a sort of statistical aggregate of all the thinking abilities.

What happens to this structure as we age? That was the question Timothy A. Salthouse, Brown-Forman professor of psychology at the University of Virginia, investigated in a new study appearing in an upcoming issue of Psychological Science, a journal published by the Association for Psychological Science. His findings advance psychologists’ understanding of the complexities of the aging brain.

“There are three hypotheses about how this works,” says Salthouse. “One is that abilities become more strongly integrated with one another as we age.” That theory suggests the general factor influences cognitive aging the most. The second—based on the idea that connectivity among different brain regions lessens with age—“is almost the opposite: that the changes in cognitive abilities become more rather than less independent with age.” The third was Salthouse’s hypothesis: The structure remains constant throughout the aging process.

Using a sample of 1,490 healthy adults ages 18 to 89, Salthouse performed analyses of the scores on 16 tests of five cognitive abilities—vocabulary, reasoning, spatial relations, memory, and perceptual speed. The primary analyses were on the changes in the test scores across an interval of about two and a half years.

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