The Web site of the American Music Therapy Association lists 57 pages of research articles published in its Journal of Music Therapy and other publications. The articles chronicle successful use of music, in combination with other therapies, to treat Alzheimer’s and Parkinson’s diseases, depression, anxiety, chronic pain, pain of childbirth, autism, and other physical and mental problems, including substance abuse. No one can tell you how music therapy works. But there is overwhelming evidence that it does. Fred Silverstone, a McLean Hospital music therapist who has studied the phenomenon, is trying to figure out why. The power of placebo, the ability of a treatment to work if a patient believes it will work, certainly is a factor, Silverstone notes. “But it doesn’t account for everything that we see,” he adds.