A long term study in brain trauma and professional fighters is underway in Las Vegas, Nevada. A preliminary paper has been published, with some sobering results.
The study concluded that the volumes of important regions of the brain and the functional connections between them were decreased in amateur and professional fighters with the most experience.
These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
There was unfortunately no distinction made between MMA fighters and professional boxers. Given the differences in rules and goals between the sports, and the vast differences in typical amateur career, grouping them does not seem rational.
Among 104 boxers and 135 mixed martial arts competitors, the number of years of pro fighting correlated significantly with reduced volume in the caudate and amygdala, and strong trends were seen toward smaller volumes in the thalamus and putamen, reported Sarah Banks, PhD, of the Cleveland Clinic's Lou Ruvo Center for Brain Health in Las Vegas.
Resting state functional MRI scans also indicated a correlation between lower connectivity between regions and the amount of fighting experience, she told attendees at the American Academy of Neurology's annual meeting.
Longitudinal data are not yet available, but Banks provided a largely qualititative overview of the cross-sectional data collected in the project so far.
The average career length at enrollment was 4 years and the mean number of self-reported fights was 11. Banks noted that the frequency of fights varied considerably, such that career length and number of fights did not correlate exactly.
Up to about year 5 of fight experience, volumes of all regions did not vary.
With experience beyond year 5, however, volumes declined -- most sharply for the caudate region of the brain. In that region, volumes were 10% lower in participants with 15 years of experience compared with those fighting for 5 years or less.
Volumes were lower by about 5% for the amygdala and putamen.
There was a lesser trend toward smaller volumes with experience in the thalamus and no hint of a relationship in the hippocampus.
Caudate volumes and years of fighting experience were more strongly related in participants who said they began fighting in earnest at age 15 or younger, Banks said. In that subgroup, caudate volumes were smaller by 0.37% for each bout reported by participants. In contrast, the reduction was only 0.10% per bout for participants who said they began fighting after age 15.
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Primary Source reference:
Bernick C, et al "Structural and Functional Brain Changes in Boxers and Mixed Martial Arts Fighters Are Correlated with Fight Exposure" AAN 2013; Abstract S54.006.