If you'd like to learn applications in music therapy, then all you have to do is sign up for a course that teaches you how to apply it, like the link futures posted previously. What it basically does is train you on how to apply the techniques into therapy, and to assess / counsel the patient / client accordingly to their needs, skimming just enough to tell you how it works cognitively on moods and stabilizing them.
If you want to study on how it all works, and research more into it, then it concerns the study of music and its phenomena towards physiological and cognitive responses combined. That said, it has -very- much to do with psychology / cognitive sciences rather than medicine as the focus tends to lie in the neuroscientific inhibitions in the brain (when and where the music is being processed, and how), and then measuring its physiological and behavioural responses to study its effects = psychology.
The applications, once there are any relevances, are then applied in the "medicinal" field.
But yeah, the panel of studies in music therapy here is very small, unfortunately. It's still lumped into alternative medicine and amidst the spectrum of art therapy. There's very little research done on them here in Singapore, and even less tolerance in using labtime to investigate it on a primary notion. Music therapy is predominantly used in combined therapy (eg. CBT, counselling, drugs, etc with music / art therapy), but is still not a widely applied form of therapy mostly because of its effectiveness in adults; there's no specific gurantee in the susceptibility of its effects because most of the adults admitted in IMH need more than just music to get by. That's why it's easier to apply it to children, where and when their brain are still being developed and are more receptive to it. In adults, the therapy is predominantly used to stabilize moods and to give a homeostatic physiological response (aka. it relaxes you or puts you in a meditative state).
Studywise, it is most notably branched out as a side-study by doctors / psychologists / psychotherapists / psychiatrists who can afford the extra time and effort into its research. It's not very popular because of the lack of scientific research compared to the treatment of drugs used to treat disorders, which has a lot more progress in its evidence and effectiveness. But personally if you asked me, I think the mental health field in Singapore is pretty much happy with relying on drugs and therapy to help one's mental health and wouldn't want to endorse much in further studies into the field.
