Scientists have found 'profound abnormalities' in scans of brain activity in a group of retired American football players.
The study into the long-term risks of the combative sport found 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," author Adam Hampshire, a neuroscientist at Imperial College London, said.
According to the Japan Times, Hampshire added that 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 toward an executive impairment in later life.
NFL games have come under growing scrutiny for what critics say is a dangerous rate of concussions after hard blows to the head.
Some have drawn links between the on field physical traumas and later neurological problems such as Alzheimer's or Parkinson's, which in turn have been blamed for depression and suicide.
The new study does not find evidence of disease, but highlights brain areas that may have been affected by repeated, severe impacts.
13 former NFL players and a comparison group of 60 volunteers were asked to rearrange colored balls in a series of tubes in as few steps as possible.
The test, called a spatial planning task, is a routine assessment of brain function.
For the first time, researchers scanned the participants' brain activity with magnetic resonance imaging (MRI) as they performed the test.
The study found that none of the 13 players had been diagnosed with a neurological condition, although all felt they were suffering neurological problems that affected their everyday lives.
The MRI scans showed huge differences in activity in the frontal lobe of the brain - the part that is responsible for 'executive', or higher-order functions.
The scans revealed "hyper activation" in parts of the frontal lobe among the NFL players, which led the researchers to conclude that the damaged brain had to work harder, bringing extra areas online in order to process the task.
"The differences seen in this study reflect deficits in the executive function that might affect the person's ability to plan and organize their everyday lives," Imperial College said in a statement.
The findings show the usefulness of MRI in revealing neurological problems that are missed by standard tests, the scientists said. (ANI )