I read elsewhere that Mr. Campbell has not lost his ability to play the guitar. I wonder if that is part of his therapy.
Motor skills are a different part of the brain from everyday cognition. It’s entirely expected that Glen Campbell could still play the guitar. Alzheimer’s patients also commonly revert to their childhood language, if that’s different from what they spoke as adults. One of my friends said that her husband used to grouch, “Why doesn’t anyone understand English anymore?!” and she would reply, “You’re speaking Spanish, Miguel.”