Lancashire, Ian. Forgetful Muses: Reading the Author in the Text. Toronto: U of Toronto P, 2010.
Read the related essay, "Vocabulary Changes in Agatha Christie's Mysteries as an Indication of Dementia: a Case Study," by Lancashire and Graeme Hirst, here: http://ftp.cs.toronto.edu/pub/gh/Lancashire+Hirst-extabs-2009.pdf.
Read Amanda Fortini's review, "Literary Alzheimer's" in the New York Times here: http://www.nytimes.com/projects/magazine/ideas/2009/#arts.
Read Judy Stoffman's review, "An Agatha Christie Mystery: Is Alzheimer's on the Page?", in The Toronto Star of January 23, 2010, here: http://www.thestar.com/news/insight/article/754723--an-agatha-christie-mystery-is-alzheimer-s-on-the-page.