For now, though, brain businesses are still more likely to lose money than to make it. The failure rate is startling even for the pharmaceutical industry, which is accustomed to tremendous risk. Ninety-two percent of drugs that enter human clinical testing for the central nervous system—basically brain drugs—flop, compared with 89 percent for drugs across all categories, according to a study in Nature Reviews, a science journal. At the same time, the total cost of bringing one C.N.S. drug to market is nearly twice the average for all drugs—$1.6 billion as opposed to $800 million. The risk, along with the generally volatile economic climate, has helped send NERV tumbling more than 18 percent since its inception last September.

Still, investors see the immense size of potential markets and have swallowed hard, pumping billions of dollars into neurotech, hoping for that giant payback. (Hit the jackpot with a new anxiety-disorder med that’s better than the current batch and has fewer side effects, and you have a potential market of 40 million Americans and 400 million people worldwide.) “People invest because a success is usually a huge success,” says Ellen Baron, a venture capitalist with Oxford Bioscience Partners in Boston, which has invested in Targacept and other early-stage neuro companies. The top 20 C.N.S. drugs each earn more than a billion dollars per year, she notes. “This new science will produce breakthroughs, and everyone feels the potential to create a truly paradigm-shifting treatment,” Baron says. “But when? Nobody knows.”

Neurotechnology as its own industry sector is the brainchild, so to speak, of Zack Lynch, a former software marketing executive who lectures widely on future business trends. He believes that we are at the beginning of a brain wave that will dominate at least the next century or two. Lynch came up with several cute names for the advances he anticipates, such as cogniceuticals, for drugs that focus on improving decisionmaking, learning, attention span, and memory processes; emoticeuticals, which influence feelings, moods, motivation, and awareness; and sensoceuticals, which can restore and extend the capacity of senses for people who have impaired vision, smell, taste, and hearing. In 2005, he and his wife, Casey, a former biotech executive, founded NeuroInsights. Later, they started the Neurotechnology Industry Organization, a policy and lobbying group that has 70 companies as members.

After several months of negotiation with a top Nasdaq official, the couple convinced the exchange to launch the NERV index in September. Its leaders include Biogen Idec, a neuro-titan with a current market cap of $19.4 billion that’s developing treatments for (among other things) multiple sclerosis and Parkinson’s, and Shire, which makes the amphetamine Adderall and has a market cap of $10.6 billion. At the even more volatile bottom are companies with market caps of $250 million or so. Only companies with more than 50 percent of their revenues coming from neuro products are allowed on the index, so big pharmaceutical concerns like GlaxoSmithKline and Johnson & Johnson, despite having blockbuster brain drugs, don’t make the cut.

J&J, Glaxo, and Lilly, however, lead the list of the top five companies in neuro­tech revenues, a group that collectively earned $30.1 billion in 2006, 25 percent of all neuro sales. Pfizer is next, with $6 billion in sales in 2006, though that is down from $8.1 billion in 2004, before its patents for big sellers like Zoloft (for depression) and Neurontin (for epilepsy) expired. Wyeth rounds out the group, with almost $3.8 billion in sales.

I meet the Lynches one afternoon at a coffee shop in the Noe Valley neighborhood of San Francisco, a block or two from the NeuroInsights world headquarters in the basement of their home. Both in their mid-thirties, the two met in a calculus class at U.C.L.A. when they were freshmen. Zack first recognized the link among companies with neural products while giving his PowerPoint presentations about the future of technology at meetings and conferences.

The Lynches tend to talk as one brain, left and right, and they agree that turning neuroscience into cash and cures requires patience. “But I think a time is coming—or may be here—when our understanding of the brain will get to the point where we can more successfully make targeted drugs,” says Casey, a petite woman with dark hair and a practical, left-brained demeanor that balances her husband’s more right-brained, pie-in-the-sky fervor. “This will profoundly change medicine, and possibly who we are,” Zack says.