Americans love our contact sports, but, unfortunately, many of them can lead to Chronic Traumatic Encephalopathy (CTE), a progressive degenerative disease of the brain most often found in athletes with a history of repetitive brain trauma, or hits to the head. CTE was so common among boxers of the 1920s, the condition was given its own boxer-related name at the time: dementia pugilistica. You're probably familiar with another term for it: "punch drunk."

Recently, a Frontline investigation highlighted research done by the Department of Veterans Affairs and Boston University in which researchers tested the brains tissue of 165 deceased NFL football players to find 131 of them showed signs of the brain disease. CTE has been diagnosed in several high-profile cases, including the suicide deaths of NFL player Junior Seau and professional wrestler Chris Benoit.

The brain of an individual living with CTE gradually deteriorates. Certain areas of the brain might shrink and atrophy, though other areas can become enlarged. The brain accumulates excessive tau protein, a substance that normally stabilizes neurons in a healthy brain. Too much tau build-up, however, can interfere with the function of neurons, causing significant changes such as memory loss, confusion, impaired judgment, impulse control, aggression, depression, and, eventually, progressive dementia. In fact, the symptoms of CTE are often misdiagnosed as Alzheimer’s or Parkinson’s at first. These changes in the brain can begin months or years after the last brain trauma. For these reasons, Bennet Omalu, a medical examiner and professor at UC Davis, recently wrote a New York Times op-ed arguing that children should not play football.