Learn about the four stages of chronic traumatic encephalopathy, or CTE, a brain disease that has been found in autopsies of many former football players, in this interactive from the FRONTLINE: League of Denial website. CTE was discovered in 2002 in the brain of former Pittsburgh Steeler Mike Webster. In its four stages of progression, changes in the brain are manifested by changes in behavior. At first, there are no overt symptoms; however, this gives way to rage, impulsivity, and depression, then to confusion and memory loss, and finally to advanced dementia. For background, watch Introduction to CTE. This resource is part of the FRONTLINE Collection.