The analogy of one’s mind as a multi-layered onion is one way of thinking of dementia . Starting in childhood, successive layers are added over the years as one acquires new memories and skills. Dementia results in the slow peeling away of the onion layers, in which the more recently acquired items are lost first, followed by the more remote memories and skills and eventually even the most basic skills including eating, walking and speaking are peeled away and lost . This process is also called retrogenesis.
A number of staging systems have been developed to help understand how the disease progresses and for making future plans. One staging system classifies Alzheimer’s Disease in three stages: early, middle and late. Another staging system, known as the Reisberg Scale, divides the disease into seven stages . The length of each stage will vary and stages may overlap.
loss of short term memory
inability to learn and recall new information
language deficits (e.g. inability to find words, lose track of conversation)
mood swings and personality changes
person can compesate for cognitive deficits and continue to function independently 
decreased long term memory
supervision and increased assistance required for ADLs and IADLs
agitation, hostility, aggressiveness, uncooperativeness, apathy
"sundowning" i.e. increased behavioural problems in the evenings such as fatigue, disrupted sleep/wake cycles
wandering, rummaging and repetitive behaviour
altered appetite, sleep and sexual behaviour
delusional thinking i.e. suspiciousness of family and friends
hallucinations may occur in 10-15% of patients 
can’t recognize self or family
complete deterioration of personality
little capacity for self care
patients eventually become bed-ridden and unable to function 
In 1995 American artist William Utermohlen was diagnosed with Alzheimer’s Disease. He began a series of self portraits that vividly portray the effect of the disease. An article in the New York Times has a number of the portraits and a slide show available. Mr. Utermohlen’s medical findings and an analysis of his work are available in a 2001 paper published in The Lancet.
4. As well as the New York Times article you may find the following accounts of his work and exhibitions interesting: http://www.galerie-beckel-odille-boicos.fr/artistes/Utermohlen/page_anglais_utermohlen.htm http://www.news.harvard.edu/gazette/2005/10.20/11-alz.html http://news.bbc.co.uk/1/hi/health/1412428.stm http://www.canada.com/ottawacitizen/features/alzheimers/story.html?id=abc81e35-40fc-49c7-a435-f4ce8d5aa1a5&k=58772