How can they possibly know, given that it can't be properly diagnosed until after death (when it's too late to be relevant for most of us anyway, though post mortem tests might be useful for research for future generations)?
My mother was still trying to continue her education until recent months, and was very sad about giving up Countdown, University Challenge, books, newspapers. I tried to persuade her it was only the malnutrition and dehydration slowing her brain down, but neither of us ever really believed it.
but (referring to the original subject, not anyone here who has replied! ) Surely it's just a matter of the mental decline being more noticeable in someone who was previously highly intelligent, articulate and/or well educated?