From a study by Milovanov R, Huotilainen M, Välimäki V, Esquef PA, and Tervaniemi M., published in Brain Res. 2007 : [online version not yet available]
The main focus of this study was to examine the relationship between musical aptitude and second language pronunciation skills. We investigated whether children with superior performance in foreign language production represent musical sound features more readily in the preattentive level of neural processing compared with children with less-advanced production skills. Sound processing accuracy was examined in elementary school children by means of event-related potential (ERP) recordings and behavioral measures. Children with good linguistic skills had better musical skills [emphasis added] as measured by the Seashore musicality test than children with less accurate linguistic skills. The ERP data accompany the results of the behavioral tests: children with good linguistic skills showed more pronounced sound-change evoked activation with the music stimuli than children with less accurate linguistic skills. Taken together, the results imply that musical and linguistic skills could partly be based on shared neural mechanisms [emphasis added].
These researchers are confirming what has been suspected for years: that the brain may reuse neural pathways which are already formed if the task is similar enough; usually this leads to a one-month advance in skills, since it takes the brain approximately a month to form and refine neural pathways.
Add enough tasks, and enough neural pathways, and you get advances of years. Although this research study focused on foreign languages, this applies to one’s native language[s], too, and therefore music lessons may decrease the amount of effort spent learning any language.