Researchers stopped treating Parkinson's Disease with brain cell transplants 14 years ago because it was largely unsuccessful and, in some cases, yielded negative side effects, like increased involuntary movement. But now they're giving an updated version of the transplant method another try, per NPR.

How it works: Parkinson's destroys cells that produce dopamine, which signals the brain's motor pathways to control how we move. Now, scientists are transplanting dopamine-producing cells into patients' brains to replace the ones that the disease destroyed. With new cells in place, the brain can control movement once again.

What's different: In the past, researchers lifted stem cells from aborted fetuses, and the samples they took contained dopamine-producing cells among several other types of cells. Viviane Tabar, a stem cell biologist at Memorial Sloan Kettering Cancer Center in New York, told NPR those extraneous cells may have caused the negative side effects. But scientists have spent the past several years figuring out how to fix this problem: they've developed a method of picking out just dopamine-producing cells from a larger stem cell sample.

Why it matters: While existing Parkinson's drugs supplement dopamine, their effectiveness can wane over time. Replacing the producer cells themselves could yield a much stronger treatment. By isolating dopamine cells, scientists can now conduct pure transplants without worrying about side effects of other cells.