Jonas Frisen had' his eureka moment in 1997. Back then, scientists suspected that there wa

s a special type of cell in the brain that had the power to give rise to new brain cells. If they could harness these so-called neural stem cells to regenerate damaged brain tissue, they might someday find a cure for such brain diseases as Alzheimer's and Parkinson's. But first they had to figure out where neural stem cells were and what they looked like. Frisen, then a freshly minted Ph. D. at the Karolinska Institute in Stockholm, was peering through his microscope at some tissue taken from a rat's injured spinal cord when he saw cells that appeared to have been enervated by the injury, as though they were busy making repairs. Frisen thought these might be the neural stem cells scientists had been looking for. It took him six years of painstaking research to make sure.

Frisen is quick to emphasize that his research is basic and that treatments are years off. But the findings so far hint at extraordinary potential. Two years ago he identified neural stem cells in the adult human brain. And he's now researching the mechanisms by which these cells grow into different types of brain cells. Rather than growing brain tissue in a petri-dish and implanting it in, say, the forebrain of a Parkinson's patient, doctors might someday stimulate the spontaneous growth of new neural cells merely by administering a drug. "It sounds like science fiction," Frisen says, "but we can already do it in mice." In 2007 he will publish the results of his recent experiments. He's isolated a protein in the mouse brain that inhibits the generation of nerve cells. Using other chemicals, he's been able to block the action of this inhibitor, which in turn leads to the production of new brain cells.

Frisen honed his analytical mind at the dinner table in Goteborg, in southwest Sweden. His mother was a mathematics professor and his father was an ophthalmologist. Frisen went to medical school intending to be a brain surgeon or perhaps a psychiatrist, but ended up spending all his free time in the lab. In 1998 he got seed money from a Swedish venture capitalist to set up his own company, NeuroNova, to commercialize his work. A private foundation tried to lure him to Texas, but Swedish businessman Marcus Storch persuaded him to stay by funding a 15-year professorship at Karolinska, eovering his salary and the running costs of his 15-person lab. "Jonas Frisen stood out from all candidates by far," says Storch, whose Tobias Foundation sponsors stem-cell research. "He is something of a king in Sweden." Two years ago two more venture capitalists helped the company expand by hiring a CEO and setting up a separate lab.

Since most researchers are interested in stem cells taken from embryos, the practice has attracted considerable controversy in the past few years. Frisen has benefited indirectly from research restrictions in the United States, which have driven funds and brain-power to Singapore, the United Kingdom and Sweden. The Bush Administration currently forbids U. S. -funded work on all but 78 approved stem-cell cultures, many of which are located outside the country. In just one sign of the times, the U. S. -based Juvenile Diabetes Research Foundation recently announced grants totaling $ 20 million for stem-cell research—the largest award yet given to the field by a medical charity—to research institutes in Sweden and elsewhere, but not in the United States.

Since Frisen doesn't work with embryonic stem cells, he's unwittingly become a champion of the radical fight, which argues that scientists ought to concentrate solely on adult stem ceils. He happens to disagree. "It would be overoptimistic or outright stupid," he says. "To really understand adult cells, we need to master how embryonic stem cells work." But what really gets Frisen going is when people ask him when they can expect a drug for Parkinson's and other diseases. "I say, five

A．weakened.

B．demolished.

C．vitalized.

D．enlivened.