In the last decade, research has shown that the brain changes in response to stimulation, and that novel and complex learning adds neurons. Less certain is the connection between rousing cells and warding off mind-robbing diseases.

Most studies have been small and have shown only limited benefits to brain training. While they have not disproved the usefulness of cerebral calisthenics, they have not proved it, either.

Results of the first rigorous clinical trial, published in December's Journal of the American Medical Association, showed that while mental exercise didn't help seniors tackle real-life tasks better, performance on certain tests improved.

"The findings are important and provocative, but not yet conclusive," said Richard Suzman of the National Institute on Aging, which helped fund the study.

Insurance company Humana has begun giving Posit Science's $395 Brain Fitness software to its Medicare Advantage customers for free — about 5,000 have requested it — and at a discount to employees. It also plans Brain Fitness Camps around the country.

The 40-hour program, based on five auditory tasks, asks users to answer questions after hearing a story or to distinguish between sounds such as "baa" and "gaa." The sound clips become progressively shorter and faster.

Skeptics wonder whether such computer programs will appeal to on-the-go boomers. "This has to get to the point of being on your cell phone," said neuropsychologist Paul D. Nussbaum of the University of Pittsburgh.

Plus, he warned, there are a lot of dubious claims out there.