Researchers at Cedars-Sinai Medical Center in Los Angeles have transplanted a man’s own brain stem cells to stop the trembling and rigid muscles that mark Parkinson’s disease. The treatment has been effective for two years, with an initial 58 percent increase in dopamine.

Other researchers are experimenting to see if brain cells can be regenerated using stem cells The study may be used in the debate over the use of embryonic stem cells. Some groups say adult stem cells can be as useful as those taken from embryos. Others say both adult and embryonic stem cells should be studied.

The researchers formed a company to develop the technique called Neurogeneration, which has been bought out by California-based CelMed Bioscience.