I watched a segment about him on the morning news about a week or so ago. On one part, he was watching an old home movie and forgot who that was when I think one of his kids or wife had to remind him that was him in the movie. At times, he'd still play on the guitar. The brain uses different parts to store memories of songs than other things.
Have you ever seen a headstone with these words
"If only I had spent more time at work" ... from "Busy Man" sung by Billy Ray Cyrus