(CBS News) -- With chronic traumatic encephalopathy (CTE) and concussions a hot topic in the NFL, a new study is adding evidence to the claims that repeated blows to the head may leave lasting effects in athletes.
Brain imaging scans of retired football players have showed unusual activity linked to how many times they had a head injury during their careers. The new study, published in Scientific Reports on Oct. 17, reports that these players may develop small neurological defects that doctors might not see with regular tests.
"The critical fact is 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," lead study author Dr. Adam Hampshire, from the department of medicine at Imperial College London, said in a press release. "This means that it is highly likely that damage caused by blows to the head accumulate towards an executive impairment in later life."
The study looked at 13 former NFL players who said they were suffering from neurological problems likely due to their time on the field. They were compared to 60 healthy volunteers.
Participants were told to rearrange colored balls in a series of tubes in as few moves as possible. During the task, their brains were monitored through a functional magnetic resonance imaging (fMRI) scan.
The NFL group performed slightly worse on the test than the control group. More troubling, the NFL group's brain scans shown unusual patterns of brain activity in their frontal lobe. The frontal lobe controls higher-order brain activity that regulates for cognitive or thought processes. The researchers believe that the changes observed may have an effect on the NFL players' abilities to plan and organize.
The differences were so stark that a computer program was able to determine with 90 percent accuracy which brain belonged to a former NFL player based on the frontal lobe activation patterns.
"The NFL alumni showed some of the most pronounced abnormalities in brain activity that I have ever seen, and I have processed a lot of patient data sets in the past," Hampshire said.
The researchers suggests the data shows that the brain may compensate for damage by having other areas work harder to make up for all the deficits. They called for more research on players, especially over the course of different seasons.
They add their work may be relevant to others outside of athletics who have suffered repeated head injuries.
An increasing amount of research has looked into how head blows sustained during football may affect the brain long-term.
Ex-NFL players were shown in a 2012 study to be especially vulnerable to deaths from degenerative brain diseases. The death rate from Alzheimer's, Parkinson's and Lou Gehrig's disease combined was three times higher for the former players than the general population. Former players are also more likely to have higher rates of depression and cognitive problems.
Then there's CTE, a progressive degenerative brain disease that often occurs in people who have had multiple concussions or other brain trauma. Symptoms can include changes in mood including depression, problems with cognition or behavior like dementia and difficulties with motor abilities. It can only be diagnosed after death.
Brain autopsies on former football players, wrestlers, hockey players, boxers, and military combat veterans revealed that the majority of them that who had repeated head trauma during their careers had evidence of CTE. Junior Seau, the former NFL linebacker who committed suicide in April 2012, was diagnosed with CTE postmortem. Interviews with family members of patients confirmed to have CTE after death revealed that their loved ones experienced symptoms that could be linked to CTE -- including "explosive" and out of control behavior, depression and memory problems -- before they passed away.
The NFL agreed to a $765 million settlement for the concussion lawsuits that more than 4,000 former players had brought forth.
A promising study in January on the brains of five retired NFL players may have found a way to diagnose CTE before the death of the person. The researchers used a PET scan and a chemical marker to look for abnormal tau proteins in their brain that normally signify Alzheimer's. But, the research is still preliminary.
Physiologist Damir Janigro of the Cleveland Clinic in Ohio pointed out that the new study had limitations, including the researchers did not compare the brains of injured NFL players to those of healthy players. It also did not look at brain function of players before their injuries. Janigro said the findings may suggest that these NFL players always had more brain function in their frontal lobe to begin with, regardless if they were hit or not.
"It could be why they are good football players," he said to LiveScience.
Despite greater awareness around head injuries and stricter guidelines before players can return to the field, many NFL players state that they would try to hide concussion symptoms even if they know it may mean bad news for their brains in the long run. The Associated Press revealed that 23 out of 44 NFL players would try to conceal a possible concussion rather than leave the game.
"The bottom line is: You have to be able to put food on the table. No one's going to sign or want a guy who can't stay healthy," Jacksonville Jaguars running back Maurice Jones-Drew said." I know there will be a day when I'm going to have trouble walking. I realize that," Jones-Drew said. "But this is what I signed up for. Injuries are part of the game. If you don't want to get hit, then you shouldn't be playing."
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