Alzheimer's pathology in the brain does not settle whether a person has dementia: the nuns' brains were full of plaques and tangles while they went on functioning normally.

Professor of psychology at UCLA

and you found that these nuns, how they aged, some of them certainly when they passed away, their brains had these kind of hallmark signs of dementia, plaques and tangles, but behaviorally they were still high functioning. So, it's really interesting that the hardware shows what we see as dementia and specifically Alzheimer's disease, but their behavior uh was that of a fairly healthy cognitive person.