The subjects of the study at McGill University were music students, who were playing their instruments and reading MUSIC simultaneously, as in an orchestra.

They compared the brain activity of these students with ones who were just playing instruments (not reading music at the same time), and also with others performing a variety of other tasks, musical and non-musical.
And the ones who were playing instruments WHILE READING MUSIC had the busiest brains.

So maybe it's only the musicians who can READ music that are a brilliant lot? Hmmmmmmmm

daylia