"This is going to explode in acceptance," he says. "It's also going to explode in the number of ways it's used and it's going to be everywhere. We're going to broadly deal with problems in the brain. This is an effort to create a juggernaut. I'm determined."

If this is a revolution, Merzenich has plenty of followers in Silicon Valley. Some prominent technology venture capitalists have invested in Posit, which got its start four years ago.

"Mike's work has deep implications for the way we live our lives," says Steve Jurvetson, a managing director of Draper Fisher Jurvetson, and the biggest investor in Posit Science. "I'd call it a growth-stage, or pre-I.P.O. company. But we hope they'll be a multibillion-dollar global company. I think the company is approaching a threshold of awareness that could take it to the next level."

Begun in October 2003, Posit Science has raised $30 million in venture capital. But its chief executive, Jeff Zimman, says it is too early to say when and if Posit Science will go public.

Posit does not disclose its financial results. But executives say the company had its first two profitable quarters this year, and the market for its software is growing. Already its product is used in "brain fitness centers" in more than 150 retirement communities across North America. They sold their first consumer version last year, and are distributing them through Humana, the second-largest health insurer in the United States.

Earlier this week, the company announced its first deal with a long-term-care insurer, Penn Treaty, which will offer the brain fitness programs to its members at no cost.

The brain-fitness program is offered on Posit's website at $395 for one user and $495 for two. The program assesses the brain's level of functionality, then continues to calibrate tasks with improvement, pushing and challenging users with harder tasks as they move forward.

For Merzenich, the road to becoming an entrepreneur began when he was a young assistant professor at the University of California at San Francisco. He met a surgeon and helped him work on a device for the hearing impaired that shocked the acoustic nerve, mimicking the electrical patterns sent to the brain to represent sound.

Science at the time held that after a period of "plasticity" in childhood, the structure of the brain became fixed. Yet the cochlear implant suggested otherwise. The device produced electrical signals that were just a crude approximation of those produced by normal hearing. But after a few months, the brain seemed to adjust.

"The brain could take the information of these crude signals and turn it into a new form of representative speech," Merzenich says. "These devices worked too well— better than we had imagined."

In the years that followed, Merzenich became a leader in a field known as "neuroplasticity." Among other experiments, he mapped the somatosensory cortex of a monkey and showed that one could quadruple the amount of area in the brain that responded to signals from the monkey's finger just by training the monkey to use the finger repeatedly to accomplish a simple task. In the same way that muscles are built at a gym, parts of the brain are shaped up by regular exercise.