Yes, there are some interesting brain synchronizations happening in music therapy and even in meditation sessions. I wrote about it here: https://medium.com/predict/beyond-words-what-happens-when-two-brains-sync-455506da67a5

For now, this sync between brainwaves shows powerful moments in therapy (like a breakthrough, or a deep connection between patient and therapist), but we haven't seen what's the biological outcome of that. As you say, maybe seeing the biological effects of these synchronizations can give us further insights into treatments for patients across a variety of illnesses including PD.