Playing music requires fine motor skills, which are controlled in both hemispheres of the brain. It also combines the linguistic and mathematical precision (which the left hemisphere is more involved in) with the novel and creative content (that the right hemisphere excels in). For these reasons, playing music has been found to increase the volume and activity in the brain’s corpus callosum - the bridge between the two hemispheres - allowing messages to get across the brain faster and through more diverse routes.
From the TED-Ed lesson How playing an instrument benefits your brain - Anita Collins
Animation by Sharon Colman Graham