Because the brain does not have sensory nerves and it is important for surgeons to make sure that they do not accidentally damage an area that controls speech or other critical functions, they can sometimes operate on patients while they are conscious. The patient is put to sleep for the surgeons to get into the skull, but then he or she is woken up to be able to respond to stimuli. Recently, a professional violinist underwent surgery to try to fix a slight tremor that was affecting his playing abilities. Surgeons woke him up and asked him to play while they were operating on him so that they could know if the problem was addressed. Modern medicine is pretty amazing!
Here's a link to the story.
Here's a link to the story.