I think I reported in a past thread that we brought a piano for mom in her room at the nursing home and even months before she died from Alzheimer's, at a point that she couldn't put a sentence together, words were just mumble, could hardly move her body of her own volition--you'd put on or take off her sweater and if you left an arm up in the air, it stayed there until we put it down manually--yet when we'd sit her at the piano she played beautifully the classics.
Nearly dead of Alzheimer's, couldn't talk, could hardly move, twisted arthritic fingers, she didn't miss hit a note.
Though at that point she also didn't play anything to completion, rather she melded all classical pieces I grew up with into a medley of memories. It was incredible for me and my brother to listen to. The transitions were hardly noticeable. I think I liked her version better.