Washington ? When aging hampers memory, some people’s brains compensate to stay sharp. Now scientists want to know how those brains make do.

This is not Alzheimer’s disease, but the wear-and-tear of so-called normal aging. New research is making clear that memory and other brain functions decline to varying degrees even in otherwise healthy people as they age. The question is how to gird our brains against time’s ravages, a question becoming critical as the population grays.

There are intriguing clues, gleaned from discoveries that some seniors’ brains literally work around aging’s damage, forging new pathways when old ones disintegrate.

High on the list: Physical exercise. It seems to do the brain as much good as the body.

A healthy brain is a bushy one. Branch-like tentacles extend from the ends of the brain’s cells, enabling them to communicate with each other. The more you learn, the more those connections form.

With normal aging, the cells don’t die but their bushes can shrivel to skinny twigs, explained Dr. Carol Barnes of the University of Arizona. Cells that are less connected have a harder time sending messages.

What’s the advice for now?

Physical exercise is the best-proven prescription so far, the scientists agreed. Memory improved when 72-year-olds started a walking program three days a week, and sophisticated scans showed their brains’ activity patterns started resembling those of younger people.

Then there’s the “use-it-or-lose-it” theory, that people with higher education, more challenging occupations and enriched social lives build more cognitive reserve than couch potatoes.

It’s never too late to start building up that reserve, said Columbia University neuroscientist Yaakov Stern. But, “the question is how. What is the recipe?”

Everything from doing crossword puzzles to various computer-based brain-training programs has been touted, but nothing is yet proven to work.