Anecdotal. My Aunt, 92, could not remember her name, address, or recognise her family. She could still sing along, even to modern songs(the theme from Neighbours was a favourite). A friend's daughter, brain damaged at birth, and unable to cope with normal lessons, nevertheless joined a ladies choirr, and was able to learn the music, words, phrasing, etc.Another friend, after a serious stroke which robbed him of his speech, was viisited by a musical friend who sang to him, and he was able to sing back in tune.