If you haven't read PG science writer Mark Roth's excellent piece on music and memory, I suggest you do so. It explains how memories relating to music tend to remain intact in Alzheimer's patients like Glen Campbell and other music-conscious individuals, long after other memories begin to fade or become intermittent. It's an outstanding piece of work that includes comments from Glen's daughter Ashley. Along with her brothers Cal and Shannon, give their dad familial support onstage during concerts, with their mother Kim taking charge offstage.
Even for those unaffected by dementia-related issues, music is a powerful memory stimulant. In 1962, when I was 11, my dad took me to a new fast food place near our home in Greensburg (the long-defunct Burger Chef on East Pittsburgh Street). A rock number was blaring as we walked in. Didn't know what it was but I never forgot it. I wasn't the music fan then that I later became and didn't care enough to figure it out.
20 years later, I heard the song on an oldies show. It was "Don't Hang Up" by the Philly vocal group the Orlons. The second I heard it, I was transported back to Burger Chef--sights, greasy french fry smells, the whole thing.
A side note: In Mark's article, Ashley Campbell revealed they don't have anything booked past August and that her dad is beginning to get tired. If the tour ends, his final US date will be in Albuquerque in June (the town where his professional career began). His final concert will be in Australia in August. That could change, but in any case, it's likely the Farewell Tour will be in power-down mode.