The corpus callosum is a cluster of nerve fibers that connect the two hemispheres of the brain. On average, the corpus callosum of musicians is larger than that of non-musicians. Compared with adult non-musicians, adult musicians who began training around the age of 7 had a particularly significant difference in the size of the corpus callosum. 
For any two musicians who start training around the age of 7, their corpus callosum is about the same size.
 music training, especially from childhood, can lead to some change in the structure of the brain.