Because other commenters weren't specific, the point is to ensure that the neurosurgeon stays away from areas of the brain that affect saxophone playing, because he'd abruptly start to mess up before permeant damage is done. In older medical dramas you'd see them do simple cognitive tests to assess the patient at various points through a surgery, this is a more advanced (albeit eclectic) method but is the same idea. Why a sax? Presumably the surgery is done in either parts of the brain associated with musical ability, or hand-eye coordination. I feel personally this is a great idea, I'd love to spend a terrifying surgery say, playing a video game, rather than literally thinking about nothing but the metal knife currently cutting into my soul. A side benefit of making the surgery safer is just gravy in my opinion.