Poorer memory and a smaller hippocampal volume were found in former NFL players with a history of concussion with loss of consciousness.
Munro Cullum, PhD, a neuropsychologist at the University of Texas Southwestern Medical Center in Dallas, and colleagues reached their findings - published in JAMA Neurology - by assessing 28 retired National Football League (NFL) players.
While anyone can suffer concussion, it is most common among athletes. According to the Centers for Disease Control and Prevention (CDC), around 1.6-3.8 million sports-related concussions occur in the US annually.
Common signs and symptoms of concussion include headache, confusion, loss of memory, dizziness, clumsiness and changes in mood.
While the majority of individuals with concussion recover within days or weeks, research is increasingly documenting the long-term effects concussion may have on the brain. In 2013, for example, a study identified concussion-related brain damage among older athletes 30 years after injury occurred.
Studies have even linked concussion to increased risk of memory conditions later in life, such as Alzheimer's disease. But according to Cullum and colleagues, the process by which concussion may have long-term implications for memory is poorly understood.
Former NFL players with concussion and MCI performed worse on memory tests
For their study, the team enrolled 28 retired NFL players aged 36-79 years. Of these, 17 reported history of a grade 3 (G3) concussion with loss of consciousness, and eight had a history of concussion and had been diagnosed with mild cognitive impairment (MCI).
The researchers also enrolled 21 healthy individuals aged 21-77 with no history of concussion, MCI or football playing as controls, alongside six individuals with no history of concussion but who had been diagnosed with MCI.
All participants were required to undergo brain scans and take part in four tests that assessed memory.
The team found that retired NFL players with a history of concussion who had not been diagnosed with MCI scored worse on tests of verbal memory - determined by the ability to remember a list of words - than control participants, though the scores were still considered normal.
However, former NFL players with a history of concussion and a diagnosis of MCI performed worse on verbal memory tests than both control participants and former NFL players without MCI.
No differences in test scores were identified between control participants with MCI and former NFL players with MCI.
Smaller hippocampal volume for older athletes with concussion, loss of consciousness
On assessing the brain scans, the team found that the volume of the hippocampus - the brain region involved in memory - among former NFL players without concussion and loss of consciousness was similar to that of control participants across all age groups.
The volume of the hippocampus among older retired NFL players with a history of at least one G3 concussion with loss of consciousness, however, was much smaller than that of control participants, while their right hippocampal volume was smaller than that of former NFL players without a G3 concussion.
The researchers also found that former athletes with concussion and MCI had a smaller left hippocampal volume than control participants with MCI.
What is more, all seven former NFL players aged 63 and older with a history of G3 concussion had been diagnosed with MCI, and of five former NFL players without a history of concussion with loss of consciousness, only one was diagnosed with MCI.
Commenting on their results, Cullum and colleagues say:
"Our findings suggest that a remote history of concussion with loss of consciousness is associated with both later-in-life decreases in hippocampal volume and memory performance in retired NFL players.
[...] Our findings further show that a history of G3 concussion in athletes with MCI was associated with greater hippocampal volume loss compared with control participants with MCI. Prospective longitudinal studies after a G3 concussion would add further insight to the mechanism of MCI development in these populations."
The team admits there are some limitations to the study. For example, they note that because they did not have access to pre-trauma imaging data for former NFL athletes, it is possible that some players were predisposed to have MCI with smaller hippocampal volume prior to playing professional football.
They also point out that previous studies have noted some inaccuracies with self-reported concussions, which could have occurred in this study.
Last month, Medical News Today reported on a study claiming the effects of concussion may differ between men and women, with women more likely to suffer ongoing memory problems.