Bill’s comment on my previous post reminded me of a book I read a few years ago, Aging With Grace by David Snowdon. The author describes what he learned about aging and especially about Alzheimer’s disease by studying a community of nuns. (Nuns make ideal subjects for epidemiological studies. They have very similar lifestyles, and so a number of confounding variables are reduced. Also, nuns keep excellent records.) The book is a pleasant mixture of science and human interest stories.
Snowdon says in his book that it is nearly impossible to accurately diagnose the extent of Alzheimer’s disease in a patient without an autopsy. Some nuns in the study who were believed to have advanced Alzheimer’s disease in fact did not. Others who were mentally sharp until they died were discovered on autopsy to have suffered extensive damage from the disease. (Snowdon tells the story of one nun in particular who was believed to be senile but who was actually quite witty. She was hard of hearing and reluctant to talk. Few people had the patience to carry on a conversation with her, but Snowdon drew her out.)
Nuns who had greater vocabulary and verbal skill earlier in their lives (as measured by essays the nuns wrote upon entering their order) and those who remained mentally active (for example, those who were teachers) fared better as they aged. They may have had more redundant mental pathways so that as Alzheimer’s disease knocked out pathways at random, enough pathways survived to allow these women to communicate well.