Brain in Alzheimer's disease. Cutaway computer illustration of a section through a human head showing a healthy brain hemisphere (left) compared to one affected by Alzheimer's disease (right). Alzheimer's 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. This image shows wasting (atrophy) of the brain cortex, as well as dilatation of the ventricles.