Bagpuss; Mental illness is a brain disease. I've been working with the mentally ill for 34 years. In that time, treatment psychiatry has come from psycho-analytic claptrap like Freud and Jung to neuro-biology. In the past fifteen years, primarily due to advances in brain scaning technology and psycho-pharmacology, we have let science take it's position as the cornerstone of psychiatric treatment. We can "look" at "well" and "ill" brains, note the differences, and administer the appropriate medications. Then we can watch the "ill" brain react, hopefully to the activity of "healthy" brains.
    In music, there is something much more sophisticated than this very crude neuro-biochemistry described above. Why do particular types of music and chord structures affect people in a particular way? Do good composers, arrangers, or conducters brains work differently? Why? This would point to diet, exercise, etc.