To support a study of the underlying mechanisms by which music may improve motor function in adults with Parkinson's disease. Clinical and related outcome measures will be taken before and after eight weeks of a non-arts intervention and after eight and sixteen weeks of group singing. Researchers hypothesize that group singing will yield improvements in clinical motor symptoms and positive changes in cortisol and inflammatory markers, and improvements in voice, breath control, and ability to swallow. The study also will analyze the relationships between motor symptoms and stress and brain activity in these adults. Additional assessment data will derive from a healthy group of adults without Parkinson's disease. The study results will contribute to a growing body of evidence about the potential benefits of music-based interventions for adults with Parkinson's disease.