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.
I read an article recently which reported the results of a study into “memory problems” in older people. IIRC they found that those with “memory problems” did better on tasks requiring answering questions about a passage they had read than those without memory problems, when those questions involved reading comprehension. The study conductors hypothesized that what seems to be memory problems may be an advantageous adaptation of the brain.
We still are a long way from understanding the brain IMO. Over 10 years ago I worked with a group studying cognitive tasks in primates and possible neurological correlates. They would isolate a single neuron in the brain area of interest and listen to is fire while the monkey performed tasks. I was amazed that they found anything meaningful at all — can you imagine trying to figure out how a computer (probably much simpler) funtions by randomly inseritng a potentiometer into the box with only the position withing the opaque box to guide you until you found something active, then recorded the voltage fluctuations as you did things with it?
However, one guy did find a neuron whose activity nicely matched the cosine of the angle of rotation of his head when images of his head at different rotations were presented to the monkey.