I am aware that the music and IQ question has already been asked. But I am not focused on IQ or intelligence here. Let me explain. Four years ago I taught myself music from scratch; I didn't know what a note was. I taught myself to compose. Even though I cannot play an instrument or sing. Four years later I can compose complex music both with staves and in a DAW. Changes I have noticed over 4 years of daily intensive music composing:  I can hear musical detail that I could not 4 years ago.  I can remember complex music easily; 4 years ago I couldnt remember any music.  I can remember and change music in my mind to new music easily.  I cannot remember lyrics anymore. Because I absorb lyrics and turn them into melody patterns instead. So I replay them as melodies that don't remove words, but create non recallable words.
Most of the four years has been spent in either Finale, a composing program, or in a DAW [digital audio workstation] called FL Studio. I have made classical, piano and electronic music. It's hard to quantify my hours spent composing over 4 years - it's been endless. Throughout it I am self taught from books; I've taken no lessons.
I can only present my experiences. I am not a psychologist or brain expert. So I have no access to studies.