Imaging correlates of memory and concussion history in retired national football league athletes
Strain JF., Womack KB., Didehbani N., Spence JS., Conover H., Hart J. Kraut MA., Cullum CM. JAMA Neurology. 2015; ahead of print
Take Home Message: Prior concussion that resulted in loss of consciousness is a risk factor for decreased hippocampal regions and mild cognitive impairment later in life.
Long-term memory dysfunction (for example, Alzheimer’s disease, mild cognitive impairment) after a concussion injury remains poorly understood and it is still debated whether concussions cause these impairments. Changes in the brain (for example, hippocampal atrophy) may be related with a history of concussions and mild cognitive impairment and learning more about these relationships may help us understand the relationship between concussions and memory impairments. Therefore, the authors measured hippocampal volumes with Functional Magnetic Resonance Imaging, performed neuropsychological tests, and collected descriptive information to determine the relationship of memory performance with hippocampal volume coupled with the influence of concussion history in 28 retired National Football League (NFL) athletes (36-79 years of age, education ranged from 15-18 years, estimated IQ ranged 92-126, 2-15 years of NFL experience, and 8 had mild cognitive impairment with concussion history). Twenty-one cognitively healthy participants were included as a comparison group for NFL athletes. The comparison group was matched for education and IQ (44-77 years of age, education ranged from 12-20 years) and had no history of concussion or past college or professional football participation. In addition, 6 age and sex matched participants with mild cognitive impairment were recruited from an Alzheimer’s disease Center for comparison with athletes who had a history of concussion and a diagnosis of mild cognitive impairment. The authors used 5 neuropsychological tests: California Verbal Learning Test, Rey-Osterrieth Complex Figure Test, Boston Naming Test, and Semantic Object Retrieval Test. Three variables were related with hippocampal volume bilaterally in athletes without memory impairments: age, California Verbal Learning Test total score, and grade 3 concussions (required loss of consciousness after concussion, 1997 American Academy of Neurology guidelines). NFL athletes with both concussion history and mild cognitive impairment performed worse on the California Verbal Learning Test compared with both control groups. The 11 retired NFL athletes who reported no grade 3 concussions showed similar hippocampal volumes compared with control participants across age distributions; however, 17 retired NFL athletes with at least one grade 3 concussion had lower mean hippocampal volumes compared with control participants. Additionally, NFL athletes with a career of 120 or more games in the NFL had a lower mean left hippocampal region compared with control participants. Athletes with fewer than 120 games did not differ from control participant’s hippocampal volume.
This study demonstrated a quantitative relationship between a history of concussion with a loss of consciousness and a loss of hippocampal volume or lower verbal memory performance later in life. The cognitive battery included many tests for cognitive impairment, but only verbal memory was related with hippocampal volume. One criteria for a grade 3 concussion is loss of consciousness, which has been associated with poorer long-term outcomes, and this study found that athletes reporting at least one grade 3 concussion demonstrated a reduction in hippocampal volumes and lower California Verbal Learning Test scores. It’s important to note that this study cannot tell us if a concussion causes these changes in the hippocampus or verbal memory performance, but can only tell us that they are related. Knowledge of hippocampal volumes and verbal memory performance prior to head injury would be interesting for future studies to help us understand how concussions effect these measures. Medical professionals should note the importance of verbal memory testing following a concussion as well as monitor athletes with a loss of consciousness and concussion history more closely for changes in verbal memory.
Questions for Discussion: Should a concussion grading system be considered again? Do you think long-term, follow-up appointments may be helpful for athletes that are at risk for poorer outcomes after suffering a concussion?
Written by: Jane McDevitt, PhD
Reviewed by: Jeff Driban