Aging baby boomers have incited a new interest in “brain fitness,” sparking an increase in businesses that claim they can impede the failing memory that so often is part of aging.

It’s not entirely a fad. There is research showing that intellectual and cognitive — that is, thinking — exercises can have positive effects on memory and reasoning. Armed with a little research and a great desire among older Americans to keep their mental abilities from declining, companies that make brain fitness software are seeing tremendous growth.

According to published reports, the American market for brain stimulation products has more than doubled, growing from $100 million to $225 million between 2005 and 2007. Some of the more popular ones are Nintendo’s Brain Age, Posit Science, Luminosity and Cogmed.

The idea behind the science and technology is pretty simple: Keep the brain active and engaged. As long as the brain’s neurons are firing, they’re not inactive or dying, and the brain replenishes itself.

Some of the programs are of the “drill and grill” variety that focus on specific exercises to aid reasoning and memory. Others are more fun-based puzzles like Sudoku, crossword puzzles and brain teasers. All are designed to make the brain work and fight off atrophy and dementia.

Brain fitness doesn’t have to be about computer games and puzzles, though. That mass of nerve cells inside your skull crackling with the activity we call thinking can begin from some straightforward life activities.

An article by Tom Zoellner on the Web site thirdage.com contends that everything from meeting people to driving home by a different route stimulates the brain. Games and computer programs can stir activity above the neck, but so can exercising your memory by recalling every detail of a person, event or conversation. Practice helps the memory function.

Avoid dull routines and add variety to your daily life: Take a different way to or from work; talk to new people and avoid the daily rut; learn something new by enrolling in a class, taking up a hobby or trying a new activity.

“An unused mind is more prone to decay than an active one,” Zoellner writes. So challenge the brain by playing games, solving puzzles.

Humor helps, too. Laughing even a little bit can stimulate the brain.

All that makes sense, and it can help stave off memory loss and halt a decline in the ability to think and reason. Plus, it can add fun and spice to life in the advancing years.

Brain fitness isn’t just for those over a certain age, either. Students use the software to help them in school, and people who have suffered brain injuries use it to recover their cognitive functions. There are also programs for people with disabilities.

So take the long way home tonight and play a few rounds of Hangman instead of watching television. Your brain will thank you. And you might remember where you put those car keys.