In Part II, chapter 7 of Oliver Sacks book, Musicophilia he states that:
Anatomists today would be hard put to identify the brain of a visual artist, a writer, or a mathematician–but they could recognize the brain of a professional musician without a moment’s hesitation.
You may be asking yourself how on earth is that possible?
Using MRI morphometry, Gottfried Schlaug at Harvard and his colleagues made careful compariaons of the sizes of various prain structures. In 1995, they published a paper showing that the corpus callosum, the commissure that connects the two hemispheres of the brain, is enlarged in professional musicians and the auditory cortex has an asymetric enlargement in musicians with absolute pitch. Schlaug et al. went on to show increased volumes in gray matter in motor, auditory, and visuospatial areas of the cortex as well as the cerebellem.