The Harvard neuroscientist Gottfried Schlaug has shown that the front portion of the corpus callosum is significantly larger in musicians than in nonmusicians, and particularly for musicians who began their training early.... Schlaug found that musicians tended to have larger cerebellums than nonmusicians, and an increased concentration of gray matter... responsible for information processing, as opposed to white matter, which is responsible for information transmission.

This is Your Brain on Music (2006)