LONDON - Scientists have found "profound abnormalities" in scans of brain activity in a group of retired American football players, adding to evidence indicating that repeated blows to the head can trigger longer-term aggression and dementia.
Although the former National Football League (NFL) players in the study were not diagnosed with any neurological conditions, brain-imaging tests showed unusual activity that correlated with the number of times they had left the field with a head injury during their football careers.
Adam Hampshire at Imperial College London, who led the study, said the ex-NFL players showed "some of the most pronounced abnormalities in brain activity" he had ever seen.
"And I have processed a lot of patient data sets in the past," he said in a statement about the research.
A growing body of scientific research shows that repeated knocks to the head can lead to a condition known as chronic traumatic encephalopathy, which can lead to loss of decision making control, aggression and dementia.
Previous research has also found that former American football players have higher rates of neurodegenerative diseases such as Alzheimer's and Parkinson's disease.
These latest findings, published in the Nature journal Scientific Reports, suggest players also face a risk of subtle neurological deficits that would not necessarily show up on normal clinical tests.
John Hardy at University College London's Institute of Neurology, who was not involved in this study, said the findings showed what he and others have long suspected - that common dysfunctional behaviour among former sportsmen such as American footballers, ice hockey enforcers and boxers is related to sub clinical brain injuries sustained during their careers.
The NFL agreed in August to pay $765 million to settle a lawsuit brought by thousands of former players, many suffering from dementia and health problems. They accused the league of hiding the dangers of brain injury while profiting from the sport's violence.