The overall arc of research on music is that it does more than soothe the savagw breast [ it mrnds the mind, provides rhythmic cues and aids in movement and balance, and singing helps with breathing and volume. Here are just three references – the third has to do with autism spectrum disorder, but what the heck, worth a read, and perhaps one can extrapolate to PD, if not generalize…
Evaluating Dancing With Parkinson’s: Reflections from the perspective of a community organization
bob's brain: living well with a movement disorder and other comorbidities 