On his website, Ian Lancashire, from the University of Toronto, reports on research done on the language of Agatha Christie and Iris Murdoch, and by way of a control informant, on that of P.D. James. He wrote a paper on the topic with Graeme Hirst, called “Vocabulary changes in Agatha Christie’s mysteries as an indication of dementia: A case study”. The paper is available through his website.
These are modern novelists, and what I was wondering about is whether it would also be possible to conduct similar analysis on letter writers, and letter writers from the past. There are some, such as Fanny Burney, for whom we have masses of material from her entire lifespan. Undigitised as yet, unfortunately. I doubt if Fanny Burney suffered from Alzheimer’s in her old age, but others may have done. Any thoughts on this?
Late Modern English letters 
In my medical intuitive practice, I have often been consulted by family and friends of those whose parents or loved ones have been diagnosed with Alzheimer’s disease. The origin of this disease is unknown, however much attention is being placed upon the growth of Amyloid plaques in the brain.Amyloid plaques are waxy and translucent protein-polysaccharide complexes that are deposited in organs or tissues during certain diseases. These deposits cause the degeneration of the organ or tissue involved. Amyloid plaques are associated with a number of conditions including Alzheimer’s disease, Hodgkin’s disease and Osteomyelitis.*
Many thanks for this information, Ernie. What we would be interested in is how to study th effects of diseases like this in the language use of people who have long been dead. Jane Austen appears to have suffered from Hodgkin’s disease, but apart from the fact that the disease could not be treated at the time, and thus led to her early death, how would it have affected her language?