Linda Hale Bucklin, a 63-year-old writer, signed up on the spot when she saw a new 'gym for the brain' in her neighborhood here. She now works out three times a week and credits a computer 'visual processing' program for helping her find her car keys faster and sharpen her tennis skills.

　　On the court, 'my game is just at a different level,' says Ms. Bucklin. 'I'm playing with 40-year-olds, and I'm holding my own really well.'

　　Vibrant Brains, the business that drew her in, has attracted about 200 members since December 2007, according to its owners. Patrons pay $60 a month to work out on 20 computer stations loaded with 'mental fitness' software, including a 'neurobics circuit' that purports to stretch the brain. Ms. Bucklin says she's addicted to an art-auction game that displays a dozen Monets for purchase. 'Then they'll intersperse them with other Monets, and you have to tell them apart,' she says. 'I minored in art history, and I still find it difficult.'

　　Thousands of Americans are choosing to join a small, but growing, number of 'brain gyms' springing up around the country. Similar brain-teaser programs are available on home computers, sometimes free of charge. The scientific jury is still out on the efficacy of such software.

　　The centerpiece of most outlets is a computer lab equipped with software from companies with names like Posit Science Corp., CogniFit Ltd., Lumos Labs Inc. and Happy Neuron Inc. Like gym rats who hit the weight machines or take Pilates classes, some users of the new technology say they prefer working with personal trainers. In this context, sessions are spent doing things like mental-fitness assessments and relaxation exercises in addition to basic cognitive training.

　　Sparks of Genius, in Boca Raton, is a Florida start-up drawing older adults with 'scientific-based brain-fitness workouts.' In southern California, a dozen 'Nifty after Fifty' fitness clubs are combining traditional exercise with time in front of computer screens, claiming that mental calisthenics work best after physical exercise. Canyon Ranch, a Tucson, Ariz.-based spa operator, has added a series of 'Memory & More' programs at its Lenox, Mass., resort, which include classes in brain nutrition, genetic workups, and cognitive training.

　　Brain exercise is spreading beyond gym walls, too. In Chicago, 'Marbles: The Brain Store' offers classes on improving mental health. The New England Cognitive Center, a nonprofit group in Hartford, Conn., is teaching trainers to take its 'Brain G.Y.M.M.' program to community centers around the country. More than 700 retirement communities have added computerized brain-fitness centers in the past three years, according to Alvaro Fernandez, co-founder of SharpBrains Inc., a firm that surveys the brain-fitness software market.

　　'We saw this area explode last year,' says Mr. Fernandez. He estimates that consumers spent more than $80 million in 2008 on mental fitness. 'You have an industry with tools and coaches. This is more real than people think.'

　　The industry pins its claims for brain exercise on a relatively new scientific discovery: neuroplasticity, the brain's ability to rewire itself throughout life by creating neural connections in response to mental activity. In a study published in 2006 in the Journal of the American Medical Association, a clinical trial involving 2,832 older adults concluded that 'cognitive training' -- such as identifying patterns in a series of letters or words -- helped improve memory and reasoning skills.