(USA TODAY) -- Poring over crossword puzzles, reading and listening to tunes may slow or delay brain decline at first, but being mentally active might speed up dementia once it hits, new research suggests.

"The person who has had a more mentally stimulating lifestyle may have more signs of disease in his brain, but the brain has been able to compensate for it better," says study author Robert Wilson, professor of neurological sciences and behavioral sciences at Chicago's Rush University Medical Center, whose research appears in Neurology this week.

The 12-year study evaluated mental activities of 1,157 people 65 years or older without dementia at the start. Participants were assessed at baseline, and then for Alzheimer's at the six-year mark. Then, every three years, they answered questions about how often they participated in activities such as listening to the radio, reading, playing games and going to a museum. They were rated on a five-point cognitive activity scale. The more often people participated in mentally stimulating exercises, the more points they tallied.

The study found that the rate of cognitive decline in people without dementia was reduced by 52% for each point on the cognitive activity scale. For those with Alzheimer's, however, the average rate of decline per year increased by 42% for each point on the cognitive activity scale.

"The rationale the authors are using is somewhat similar to what people call 'cognitive reserve,' " says Ron Peterson, director of Mayo Clinic's Alzheimer's Disease Research Center.

He says the theory is that in the active mind, the brain creates new neural pathways when damage occurs to circumvent the problems.

Alzheimer's expert Steven DeKosky, dean of the University of Virginia School of Medicine, uses this metaphor: The active brain is like a piece of good wood that's been varnished and revarnished over the years. The inactive brain has fewer coats or lower-quality varnish, he says.

"You don't get symptomatic until you sand down to the bare wood," DeKosky says.

Wilson says researchers don't fully understand why active-minded people suffer such a rapid decline once they develop Alzheimer's, but the study shows the advantages of using your brain because of the early benefits.

That the active-minded person spends less total time in a cognitively disabled and demented state is "a universal good thing," Wilson says. "It's good for the affected person, good for their family and friends and good for our public health system."

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