It's always a little freaky to watch videos of awake brain surgery: It's hard to believe that someone can stay calm and patient as doctors slice into their heads, and there's something macabre about watching them talk through the process.
But that's important -- these patients are kept awake precisely so that they can speak or perform other high-level functions as surgeons work on them. They're giving doctors a map to work with when it comes time to remove the actual tumor.
The 12-minute video above, which was taken in June 2014, shows professional opera singer Ambrož Bajec-Lapajne singing Franz Schubert's "Gute Nacht" during his own surgery.
In Bajec-Lapajne's case, doctors kept him awake during his craniotomy as they wanted to monitor his ability to recognise changes in key, since that's something he relies heavily on for his profession. They were most likely trying to avoid hurting those functions in the course of removing the tumor. Singing is also a good task to help doctors avoid hurting speech areas -- which is why some musicians choose to play guitar and sing during their surgeries instead of more traditional tasks like reading and answering questions.
You'll see something alarming happen around the 2:40 mark: Bajec-Lapajne slurs his words, and his singing slows to a muddy halt. But that's not an indication of something going wrong, exactly: Surgeons need to know what parts of the brain will wreak this kind of havoc if they're interfered with. Bajec-Lapajne's scary moment was exactly the point of the exercise, showing surgeons where not to go during the tumor removal.
And as you can see, he bounces right back to a beautiful performance. Bajec-Lapajne writes on his YouTube page that he's doing fine a year later, and continues to pursue a career in classical music.