I spent several years working with Alzheimer's patients in various capacities (as a CNA, as an art and recreation therapist and as a nursing student on clinicals) and I have long held the theory that sleep deprivation throughout life is one of the foremost hidden causes of it. A couple of your links are now suggesting that I might not have been blowing smoke up myself after all. Maybe I should have published.
Something else I noticed for what it's worth is that they remember the music of their youth even when all else is lost :( Aways found that so ... bittersweet, I guess, is the word.