Healthy brain (left) and brain in Alzheimer's (right), illustration. Alzheimer's disease is a neurodegenerative disease and a common cause of dementia in the elderly. It is caused by the formation of protein plaques in the brain, which kill surrounding neurons. The cause of these plaques is not known and there is no cure. The progression of this degenerative disease causes atrophy in both halves of the brain, seen here as a reduction in size, change in colour, and increased amount of blood vessels.