A reduction in brain oxygen supply due to ANOXEMIA (a reduced amount of oxygen being carried in the blood by HEMOGLOBIN), or to a restriction of the blood supply to the brain, or both. Severe hypoxia is referred to as anoxia, and is a relatively common cause of injury to the central nervous system. Prolonged brain anoxia may lead to brain death or a persistent vegetative state. Histologically, this condition is characterized by neuronal loss which is most prominent in the hippocampus; globus pallidus; cerebellum; and inferior olives.