It's 1 p.m. at the Heritage Estates' Brain Gym in Livermore, Calif., and the gym rats are starting their workout.

Dorothy Emmrich, age 100, straps on a headset and glares at a computer screen showing rows of playing cards. Each makes a different sound when she clicks on it. She searches for pairs that make matching sounds, a classic memory game.

The software was created by closely held Posit Science Corp. in San Francisco. It is one of about 20 companies, including Nintendo Co., pitching brain games to the elderly and baby boomers to delay or blunt the onset of dementia. The market will surge to $2 billion by 2015 from $225 million last year, says Alvaro Fernandez, co-founder of SharpBrains, a San Francisco consulting company.

"This is a whole new subindustry — exercise equipment for your brain," says Andrew Carle, an assistant professor at George Mason University in Fairfax, Va. "If Suzanne Somers could make millions of dollars off the ThighMaster, think what you could do with brain-trainers."

Insurance companies including Humana Inc., the second-largest seller of Medicare drug plans, are encouraging policyholders to use the games. Treating Alzheimer's and dementia patients in 2005 cost the U.S. government's Medicare and Medicaid health programs $112 billion, a total that will reach $184 billion by 2015, according to the Alzheimer's Association.

About 5.2 million people in the U.S. already have Alzheimer's — a progressive and fatal disease that destroys brain cells — and 10 million baby boomers eventually will develop it, says the association, based in Chicago. Americans older than 55 fear they will develop Alzheimer's more than any other illness, according to a 2006 MetLife Foundation survey.

Brain-training programs for the elderly "will become as common as bingo," says SharpBrains' Fernandez, 35, whose company promotes science-based cognitive training. "Over 400 senior residential facilities have brain-fitness centers today."

People who choose activities that stimulate their minds throughout their lives are less likely to develop dementia, or memory loss, says Robert Wilson, a neuropsychologist at Rush University Medical Center in Chicago and an early researcher in the field.

There's little evidence that one type of cerebral exercise is better than another, he says.

"If I was going to bet on anything, I would bet on reading," says Wilson, 60. "The key is to pick something you enjoy and can sustain over a long period of time."

People older than 65 who spent an hour a day for eight to 10 weeks using Posit's Brain Fitness program performed better on mental acuity tests than a group that spent the same computer time on educational programs, according to a study the company funded and conducted with the Mayo Clinic in Rochester, Minn.

Humana, based in Louisville, Ky., sells the Posit product to its members for $100 instead of the usual $395, says Tom Noland, a Humana spokesman. Penn Treaty American Corp., in Allentown, Pa., a long-term care insurer, also offers the product to policyholders, says Stephen LaPierre, senior vice president for claims management.

Dementia is the most costly source of claims for long-term care insurers and one of the two most common, LaPierre says.

Posit, founded in 2002, made money for the first time in the first quarter of 2007, says Chief Executive Officer Jeff Zimman, 51, who declined to provide details.

"This is the earliest stage of a new market," Zimman says.

Nintendo, the world's biggest maker of portable game players, sold 21.5 million copies of its Brain Age and Brain Age 2 games in the past two years.

The games, marketed as "mental workouts," help Nintendo, based in Kyoto, Japan, reach older customers, says spokeswoman Amber McCollom.

"Nintendo has never claimed to improve anyone's health with any of the brain games," McCollom says.

Dakim Inc. in Santa Monica, California, sells a product called (m)power, marketed to centers for the elderly as a "cognitive fitness system." Competitors including Lumos Labs Inc. in San Francisco and Eons Inc. in Boston are developing Internet-based brain exercise games for boomers.

"They're forgetting where they left their car keys, and simultaneously they're taking care of their 80- and 85-year-old parents who have Alzheimer's, or some other kind of dementia," Carle says. "They're looking into the future and they're worried."

The Posit program is built on the notions that the brain and its wiring are malleable and that certain kinds of experiences can trigger structural benefits, according to Michael Merzenich, 65, a University of California, San Francisco, neurologist who co-founded Posit and helped pioneer the concept of brain plasticity.

"The revolution has occurred in understanding that the machine is massively rewiring itself every time you acquire a new skill or ability," Merzenich says of the brain. "That plasticity is in place to the end of life."

As the brain ages, its ability to process information declines, Merzenich says. For most people, the drop-off begins in their 30s, with a dramatic decline in their 60s.

In Merzenich's view, the only way to reinvigorate the brain is through continued learning. That stimulates neurons, the nerve cells that carry messages in the brain, to fire and form new branches. Solving crossword puzzles or playing bridge keeps the mind active but doesn't make it perform new tasks, he says.

At the Livermore brain gym, a small carpeted room with computers and photos of brain-training graduates in caps and gowns, Kit Spickard, 76, uses her fingers to count out sounds so she can recall the order in which she heard them. She answers correctly and a cartoon appears of a train carrying hamsters along a track. The reward stimulates the brain to crank out chemicals like serotonin and keeps players motivated, Merzenich says.

The mental exercises are working, she says. "If I leave my shopping list at home, I find I didn't need it anyway," says Spickard.