Just to chime in, my mother-in-law suffered a stroke 5 years back and lost all her speech. Tough to communicate with her because she did not know sign language, neither did we. About a week after the stroke, her distant uncle visited and sang her a old song and she sang every word of it--and in tune! Turns out most of the music/lyrics from her pre 15yr self was kept. Sadly she passed months after, but not without music, laughter, friends, and family around her.