Exercising to keep aging at bay

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    Mental exercise games are being claimed to slow brain aging, but the evidence for this idea is not yet conclusive.


    Earlier this year, Nintendo launched the American version of a game for seniors called “Brain Age: Train Your Brain in Minutes a Day.” Developed in collaboration with Japanese neurologist Ryuta Kawashima, this game is based on the idea that regular mental exercises—such as Sudoku puzzles, Stroop tasks and simple math problems—can keep aging brains sharper. Similar games are being developed by other companies intent on capturing this new market. Radica, a subsidiary of Mattel, is releasing “Brain Games,” word and memory games based on research at the University of California at Los Angeles Center of Aging. Another company, MindFit, is also marketing cognitive training games for seniors, citing extensive evidence for the 'use it or lose it' theory of cognitive decline with aging. Despite the marketing hype, there is no conclusive evidence that mental games alone slow brain aging.

    As people age, their performance declines on many tasks, particularly those involving working memory, and they lose some brain volume. Older people also show less activation than younger adults in brain imaging studies during a wide variety of tasks. Positron emission tomography shows broader recruitment of different brain areas in older adults during specific tasks. However, it is unclear whether this change reflects failure to recruit specific neural processes or compensation for lost neural function.

    Animal studies indicate that environmental factors such as enrichment or physical exercise may affect cognitive function and slow down certain markers of aging. Rats housed in enriched environments show increased dendritic branching and neurogenesis, but how these findings relate to changes in cognition is unclear. In any case, long before buying their first video game, almost all humans live in an enriched environment compared to most laboratory animals, so it remains uncertain whether additional enrichment leads to further improvements. Physical activity is also linked to enhanced performance on cognitive tasks, which has been attributed to exercise-induced increases in neurotrophic factors or to enhanced vascularization in the brain.

    Extrapolating the results to humans, though challenging, seems to confirm this trend for physical fitness. A meta-analysis of aerobic fitness training studies in aging found significant effects on cognition, particularly on tasks involving executive control processes1. Recently, a six-month randomized clinical trial split older adults into two groups, one that received aerobic training and another that did stretching and toning (nonaerobic) exercises. After training, the aerobic group showed increases in both gray and white matter volumes2. However, the consequences of increased volume for cognition are not conclusive, and there remains no clear evidence correlating different levels of physical activity to performance.

    The data linking mental training to amelioration of age-related cognitive decline are murkier. Most people, young or old, improve their performance on tasks with practice. Some studies suggest that cognitive training improves mental ability. A randomized control trial with 2,832 seniors reported that as few as ten sessions of cognitive training improved performance on tested tasks even five years later3. Participants also reported a higher confidence in being able to handle their day-to-day tasks, though self-report is not the most reliable measure of improvement in real-life activities or ability to live independently. In another randomized controlled study4, adults in the Posit Science Training program, who performed increasingly difficult auditory stimulus recognition, discrimination and memory tasks, showed improvements in the specific tasks as well as on a global auditory memory test. However, other studies have found little evidence for a slower rate of age-related decline in reasoning in individuals who spend more time doing mentally stimulating tasks such as crossword puzzles5.

    Generalizing from these studies is difficult. Does solving crossword puzzles or doing auditory discriminatory tasks improve real-life tasks and independent living? At every age, cognitive performance varies substantially among individuals. Some variability in cognitive ability during aging may be present at earlier ages as well and thus may not relate to differential aging5. The ideal way to test this hypothesis is in a randomized clinical trial, carefully controlled to show that individuals who start out at the same mental level show a shallower rate of age-related decline with greater mental stimulation relative to their peers who have less mental stimulation. Such studies are almost impossible to do, because people would have to maintain an assigned lifestyle for much of their lives. Quantifying cognitive fitness is also challenging, as is separating social factors from cognitive stimulation.

    What is clear is that the public is unwilling to wait for careful validation of the science before embracing a magic bullet purported to delay aging. It would be unrealistic to expect that companies should refrain from marketing these programs to seniors until they have been rigorously validated, but at the minimum, companies should publish controlled trials with their products in peer-reviewed journals. Seniors who pay for these programs deserve to know if they work.

    Most scientists would argue that there is no harm in keeping physically fit or cognitively challenged, and that the only downside to such programs is a dent in your wallet. Still, there is an inherent danger in conferring scientific credibility on products that may not live up to their claims. Instead of investing in these cognitive programs (or even a future video game akin to the Nintendo Wii that combines physical activity with mental exercise), grandma may be better advised to take regular walks, stay socially active and challenge her mind without the aid of commercial games.

    View more background material on Connotea at http://connotea.org/user/NatNeurosci/tag/editorial200703


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