“The brain is 86 billion neurons,” Nowinski said in a telephone interview. “We’re talking about somewhat microscopic lesions here and there. The location of the lesions and how your brain is wired will probably have more of an impact than the staging. A lesion that’s a millimeter in the other direction could be the difference between normal behavior and impaired behavior.”
Stage 1 is the earliest sign of C.T.E. The lesions are found primarily in the frontal lobe, and symptoms often include slight memory loss. In Stage 2, the lesions spread to the adjacent cortex, continuing their assault on memory. Frontal lobe damage, Nowinski said, is well-known to be associated with concentration, cognition and impulse control issues. The examination of Adams’s brain, which was found to have Stage 2, indicated an abnormally severe diagnosis for a person in his 30s, akin to that found in Hernandez, whom McKee diagnosed with Stage 3, in which the lesions have taken over the medial temporal lobe, affecting the hippocampus and amygdala, and causing impulsive, violent reactions; paranoia; and the erosion of memory.
In Stage 4, when the C.T.E. has spread to multiple parts of the brain, Nowinski said, the vast majority of people have been clinically diagnosed with dementia. He said that 13 years tends to elapse between stages and that people over 60 with C.T.E. almost always are found to have Stage 3 or 4.
What has been C.T.E.’s impact on the N.F.L.?
The Hall of Fame center Mike Webster was the first N.F.L. player found to have had C.T.E., with the result published in a scientific journal three years after his death in 2002. More than 315 former players, including Ken Stabler and Frank Gifford, have been posthumously diagnosed with C.T.E. Researchers at Boston University announced in a 2019 study that tackle football players doubled their risk of developing the worst forms of C.T.E. for each 5.3 years they played.
For many years, the N.F.L. denied any connection between long-term brain damage and blows to the head until confronted with overwhelming scientific evidence. When a class-action lawsuit brought by former players surfaced, the league acknowledged the connection and agreed to a roughly $1 billion settlement; the N.F.L. has since agreed to stop using race-based methods in evaluating dementia claims that denied benefits worth potentially hundreds of thousands of dollars to Black players.
In response to the rising prevalence of C.T.E., the N.F.L. has developed intensive protocols for players who have, or show signs of, a head injury. The league installed a head-injury spotter in the press boxes of all games; doctors and neuro-trauma specialists on the sideline; and experts in neuro-cognitive testing in the locker room. The league has also strengthened rules against hitting quarterbacks and players who lower their helmets to initiate contact.
The N.F.L. has invested hundreds of millions of dollars in helmet and concussion research, and even staged a $3 million grant competition intended to improve helmet performance and safety. According to the league, 99.9 percent of players wore what it considered a “top-performing helmet” last season, and it is hoped that position-specific helmets will be introduced soon.