Healthy and Alzheimer's neurons. Computer illustration comparing a healthy brain neuron (nerve cell, top) with one from a brain affected by Alzheimer's disease (bottom). Alzheimer's is caused by neuron and synapse degeneration and the formation of protein plaques (blue, bottom right) in the brain. This abnormal loss leads to atrophy (wasting) of the affected areas. Symptoms include memory loss, personality changes and confusion.