It was a homespun truth passed down for generations that people are born with all the brain cells they will ever have. Over time, through age, injury or too much drinking, it was thought we could only stand to lose them.

But Canadian scientist Samuel Weiss turned that age-old dogma on its head. During a 1989 lab experiment at the University of Calgary, Dr. Weiss accidentally discovered that the adult brain can indeed produce new cells - stem cells, which, like seeds, can even grow into neurons.

The finding immediately raised the prospect of regenerating damaged nerves with stem cells the brain can produce itself. More recently, it has led to new research into the role stem cells play in forming memories, and the role abnormal stem cells play in brain cancers and mental illness.

The 52-year-old Dr. Weiss is one of this year's winners of the prestigious Gairdner award for medical research. Launched in 1959 by Toronto businessman James Gairdner, the annual Canadian biomedical awards have also come to be known as the "baby Nobels," because 70 of the 288 recipients in the past 49 years have gone on to win the big Swedish prize.

"I was blown away by the news," said Dr. Weiss, a U of C professor of cell biology and anatomy.

"At the time, you don't really understand the full implications of what you've found until it can be evaluated and studied by others."

Dr. Weiss and graduate student Brent Reynolds had originally been looking for natural proteins to keep brain cells alive when they realized they had stumbled on a culture that coaxed the growth of new immature brain cells. They had so doubted their own findings that they repeated the accidental experiment "100 times to convince ourselves."

Five other scientists will also receive the $30,000-medical research prize from the Gairdner Foundation this year. Foundation president Dr. John Dirks said the winners have made "outstanding achievements in the most promising areas of medical discovery."

The recipients, for example, include Harald zur Hausen, scientific director of the German Cancer Research Centre in Heidelberg. During pioneering research in the 1970s and 1980s, he discovered that the human papilloma virus causes cervical cancer. That work led directly to the creation of the HPV vaccine, an injection now widely administered to girls and young women to protect them from contracting the cancer-causing virus.

Victor Ambros, a professor of molecular medicine at the University of Massachusetts, and Gary Ruvkun, a genetics professor at Harvard Medical School, have also been named Gairdner winners for their 1993 discovery of micro-RNAs. These small strands of genetic code, produced by DNA, have the ability to regulate, or actually turn off, a gene. They have since become crucial targets for research into illnesses including cancer, heart failure and diabetes.

Along with Dr. Weiss, two other Canadians are among this year's winners. One is Nahum Sonenberg, a biochemistry professor at McGill University, who has long studied how DNA translates its code into the proteins that make up the human body and make it function.

The Gairdner Foundation wrote that Dr. Sonenberg's work on protein synthesis has "led to the possibility of developing cures for diseases, including cancer, obesity, memory impairment and virus infections."

The foundation has also awarded Alan Bernstein, executive director of the Global HIV Vaccine Enterprise in New York, the 2008 Gairdner Wightman prize for his "outstanding contribution to Canadian health research." Dr. Bernstein is the inaugural president of the Canadian Institutes of Health Research, the federal agency largely responsible for funding medical research in the country.

In its February budget, the federal government announced a $20-million endowment for the Gairdner Foundation, which will see the prize money given to each recipient jump to $100,000 starting next year, the 50th anniversary of the awards.