Sci. Aging Knowl. Environ., 17 September 2003
Ups and Downs
The brain retains its complexity, even in old age
Key Words: longitudinal cross-sectional factorial invariance Wechsler Adult Intelligence Scale (WAIS-R)
Some people dread getting older, imagining that the first signs of forgetfulness presage the loss of all their hard-won skills. Others take a more hopeful stance: Although they might lose their lightning reflexes, say, they'll hold on to their way with words or their ability to piece together a jigsaw puzzle. Psychologists debate which vision comes closer to the truth, and a new paper supports the second notion, showing that older people retain their relative strengths and weaknesses rather than deteriorating across the board.
Traditionally, cognitive tests have suggested that a person's variations in mental facilities flatten out with age. According to a classic hypothesis called dedifferentiation, as memory, verbal proficiency, and math skills slide downhill, the differences between them eventually disappear. However, recent studies have challenged this concept, suggesting that age affects different abilities differently; some decline rapidly, others less so--and some even improve, presumably to compensate for the declines (see "All in Your Mind"). For instance, sensory functions such as vision, and motor skills such as reaction time, deteriorate sharply with age. Yet the speed with which older people perform certain tests requiring visual and motor skills--such as viewing a string of letters and pressing a button if it forms a word--decreases less than would be predicted by these shortcomings. Therefore, researchers conclude, senior citizens must outpace their younger counterparts in the central processing arena, the brain activity that translates sensory input to motor output. Such results have challenged the dedifferentiation hypothesis by demonstrating variation in how age affects different cognitive functions.
To glean a clear picture of how abilities change in relation to each other over time, mental health researcher Kaarin Anstey of Australian National University in Canberra and her colleagues recruited more than 1800 participants ages 65 and up, divided them into groups by age, and assessed their skills using a battery of tests that measure memory, verbal ability, and mental speed. They retested everyone 2 years later and then again after another 4 years. Then the investigators looked at how closely related the tested abilities were at each point in time within each age group. Contrary to predictions from the dedifferentiation hypothesis, the researchers found as much variation in the oldest group's test scores as in the younger groups'. Furthermore, variation among different abilities within individuals did not decrease with age, providing firm support for the hypothesis that age affects different mental processes differently.
"This is a much more positive view of aging" than the dedifferentiation hypothesis, says cognitive psychologist Philip Allen of the University of Akron, Ohio. The new results, he says, support the idea that different factors underlie declines in the different cognitive areas, as opposed to the traditional view that one common cause drives mental aging across the board. Allen praises the study's thorough statistical analyses and large sample size, which lend weight to the conclusion. The new data point to a high degree of complexity in the aging brain, which should prompt researchers to investigate the individual causes underpinning different areas of decay.
September 17, 2003
Science of Aging Knowledge Environment. ISSN 1539-6150