When a Rutgers psychologist, Paula Tallal, approached Merzenich and said she wanted his help applying neuroplasticity to children who had trouble processing information, he jumped at the chance. Merzenich created a training program that diagnosed a baseline of functionality, then gradually built up the areas of the brain associated with information processing. Tallal tested it out on children.

"By the end of the summer, we couldn't believe how different they were," Merzenich says. "One little kid was five and had the language skills of a two-and-a-half-year-old. A month later, his language was almost age appropriate. I knew at that point we had a valuable invention. I knew it would be commercialized."

After the clamor created by the Science article, Merzenich's chancellor at U.C.S.F. formed a committee to explore ways to bring the technology to market. Merzenich found himself facing Charles Schwab, the founder of the giant discount brokerage firm, and other business leaders on the committee, and soon realized some difficult challenges lay ahead.

"I had written a 12-page paper on how wonderful the science was and called it a business plan," Merzenich recalls. "Schwab started saying all these things I didn't understand. You don't know what kind of product you have, how to market it."

Merzenich was soon learning on the job. He took a sabbatical and served as president and chief executive of Scientific Learning for a year and a half, before returning to the university and staying on with Scientific Learning as a scientific adviser and member of the board.

Scientific Learning went public in 1999, near the height of the technology boom, at $16. The shares now trade at about $6.

Still, by most measures the company has been successful. But Merzenich chafed against the limitations imposed by having shareholders. As C.E.O., for example, he spent about $11 million evaluating how the neuroscience could help other populations. But the company decided it could no longer afford to focus on populations tangential to its core mission.

The unfinished research kept gnawing at Merzenich. So in 2002, Merzenich recruited Zimman, a lawyer with a venture capital background, to help him launch a new company. Merzenich's vision was for a broad company that would focus on many areas. Zimman suggested they begin with just one, and expand from there.

"Some scientists are motivated by fame, some by fame and money. Mike's pretty unusual in that what he really wants is to get the science out into the world," says Zimman, who became the chief executive.

They chose to focus on healthy aging, since the likelihood of success seemed the strongest.

"There's so many opportunities with this technology that we should constantly be moving ahead with other areas," Zimman says. "We've barely started with healthy aging and we're moving ahead with other clinical areas."

For now, Merzenich believes the emerging field of "brain health" is cluttered with bad science. He singled out Nintendo's brain games as an example of a product that has no science to back up its claims. But he doesn't expect that to last.

"This field is undisciplined now and full of trash," he says. "But it will mature and ultimately the snake oil will be cleaned up. It will grow like the fitness industry from almost nowhere. And it will become a part of everyday life."