Scans have revealed "profound abnormalities" in the brain activity of retired American football players, a study into the long-term risks of the combative sport said on Thursday.
Unusual activity in the frontal lobe, observed in former National Football League (NFL) players as they carried out a cognitive test, matched records for heavy blows they had received to the head while on the field.
"The NFL alumni showed some of the most pronounced abnormalities in brain activity that I have ever seen," said lead author Adam Hampshire, a neuroscientist at Imperial College London.
"(The) level of brain abnormality correlates strongly with the measure of head impacts of great enough severity to warrant being taken out of play. It is highly likely that damage caused by blows to the head accumulate towards an executive impairment in later life."