Yes, I’d heard of this effect on a news story not too long ago. I originally found on the funny news aggregator site called Fark. (Please don’t browser there unless you know what you’re doing.)
Some African-American caregiver was prevented from suing for discrimination because it was the facilities policy to accept the fact that, as dementia sets in and advances, people lapse back into their Jim Crow-era behavior. Basically she was dinged for not giving care to a woman who had fallen, because that woman insisted on not being touched by Black people, and there was a delay in getting the help that was needed. So bad news all around.
Now, first off I don’t have a citation. And this is simply the institutions policy, so I didn’t say I agreed with it, that’s a great debate territory. But, if you can find a news story with the facts I gave you, you may find in the news story, the name of the institution, and they may have a professional that they site to give an opinion on the subject.
Obviously, everyone experiences their declining years differently. I don’t think a sudden onset of racism or bigotry is a warning sign in and of itself. More along the lines of: having diagnosed the condition, you can now expect – old attitudes to resurface, including … bigotry, racism, sexism, yadda yadda