""We've found compelling evidence that musical interventions can play a health-care role in settings ranging from operating rooms to family clinics," says Levitin, author of the book "This is Your Brain on Music" (Plume/Penguin, 2007). The analysis also points to just how music influences health. The researchers found that listening to and playing music increase the body's production of the antibody immunoglobulin A and natural killer cells — the cells that attack invading viruses and boost the immune system's effectiveness. Music also reduces levels of the stress hormone cortisol."