Illustration of a brain. The left side is normal and healthy. On the right side is a brain with the Alzheimer's disease. Alzheimer's disease is a neurodegenerative disorder. It is the most common cause of dementia. Affected persons have protective intellectual deteriorations and behavioral changes. Special neurons are degenerated. The amount of brain is reduced. It is shown on this picture on the right side. There are few neurotransmitters, blue on this picture.