Research on animals and humans suggests mentally challenging activities such as playing bridge, learning a new language or even blogging might help build new connections in the brain, says Molly Wagster at the National Institute on Aging, part of the National Institutes of Health.

To get the most benefit, Fordyce suggests seniors pick an activity that provides them with a challenge, such as learning a language or taking classes at the local university or senior center. Even learning to use a computer or a cellphone can be a challenge for someone who has never used the latest gadgets before, she says.

Seniors who join a book club or some other social activity must use their brain to interact with other people and that seems to shield it from a decline in function, Fordyce says. Researchers don't know whether regular social contact builds a better brain or simply reduces stress, which can harm the brain.

What the research can't offer is a one-size-fits-all prescription. Albert says seniors should pick activities they enjoy.