Gottgfried Schlaug, MD, PhD, et all from Harvard Medical School and Boston College  found that taking music lessons can strengthen connections between the two brain hemispheres in children, but only if they practice diligently. For the children who practiced at least 2.5 hours a week, a portion of the corpus callosum that connects movement-planning regions on the two sides of the brain grew about 25%. (Miller, Greg. Science NOW Daily News 2008.