“For the first time, there’s a clear path forward,” said Eric Lander, the president of the Broad Institute.

Experts not affiliated with the institute or the new paper agreed that the news on both fronts was good, but characterized the research as a first step in a long process. “The signals they found are real signals, period, and that is encouraging,” said David B. Goldstein, a Duke University geneticist who has been critical of previous large-scale projects. “But at the same time, they give us no mechanistic insight, no targets for drug development. That will take a lot more work.”

Jonathan Stanley, now 48, cannot explain why he suddenly developed bipolar disorder at 19. All he knows is that his brain responded well to lithium. He was eventually able to return to college, complete law school and become a lawyer. “You’re talking to a guy who went from psychotic to normal with some pills,” he said.

When scientists began to discover psychiatric drugs like lithium in the mid-20th century, they did so mostly by accident, not out of an understanding of the biology of the diseases they hoped to cure. For many years, they worked backward, hoping that by figuring out the action of the drugs, they could understand the causes of the diseases. But they came up empty.

Some researchers argued that a better strategy would be to find the genes involved in psychiatric disorders. This approach would give them new molecular targets for drugs they could test.

Yet the staggering complexity of the brain has yielded few secrets. More than 80 percent of the roughly 20,000 genes in human DNA are active in the brain.