Unfortunately, scientists do not yet know the answer to this question. Some theories scientists are testing include the idea that certain neurons (such as dopamine neurons in the midbrain, which are lost in Parkinson disease) have an incredibly high energy demand and metabolism. Because some of these neurons work extremely hard, any slight change in their health (like proteins abnormally sticking together inside the cell) may cause them to die. However, compared to other cells in the body, all neurons in the brain have a relatively high energy and oxygen demand and high metabolism. It is still unclear why certain neurons die while others can live under the same stressors, such as disease.