Scientists in Sweden say they have made a “huge breakthrough” with stem cell research that may dramatically improve the treatment of Parkinson's disease. Parkinson's is brought on when brain cells stop producing dopamine, a chemical that controls mood and movement. Scientists simulated Parkinson's in rats and then converted human embryonic stem cells into neurons that produced dopamine. Evidence showed that at least some of the Parkinson's brain damage was reversed. Although there have been no human clinical trials of neurons derived from stem cells, they may begin as early as 2017.