A study of 202 deceased football players’ brains has found that 87% of participants demonstrated features of chronic traumatic encephalopathy (CTE), a neurodegenerative disease linked to repeated head trauma. 99% of the National Football League (NFL) players in the study demonstrated the same CTE features. The brains studied were donated for research following the football players’ development of mental symptoms prior to death.

According to Science magazine, the study found that “whether the men’s brain changes were mild or severe—all experienced mood, behavioral, or cognitive symptoms associated with CTE. These included impulsivity, depression, apathy, anxiety, explosive rages, episodic memory loss, and problems with attention and higher order thinking.” The findings may “ratchet up the pressure on leaders at all levels of football to protect their players,” Science contextualized. “Still, the authors and other experts caution against overinterpreting the results, because the brains all came from symptomatic former players and not from those who remained free of mental problems.”

Partly funded by a $30 million donation by the NFL to the National Institutes of Health from 2012, the study was spearheaded by Boston University neuropathologist Ann McKee. She stressed the skew of the results towards features expressed by symptomatic male college or professional football players, as opposed to asymptomatic individuals or those who played exclusively on less intense types of teams.

Though the applicability of its findings are still limited, the study is the largest of its kind to date. Signalling the depth of research necessary to elucidate the impact of head trauma in football players, the study foreshadows the NFL and public policy shifts that may become necessary following future research developments.