Repeated head trauma is associated with smaller thalamic volumes and slower processing speed: the Professional Fighters' Brain Health Study

Abstract

Objectives: Cumulative head trauma may alter brain structure and function. We explored the relationship between exposure variables, cognition and MRI brain structural measures in a cohort of professional combatants.

Methods: 224 fighters (131 mixed martial arts fighters and 93 boxers) participating in the Professional Fighters Brain Health Study, a longitudinal cohort study of licensed professional combatants, were recruited, as were 22 controls. Each participant underwent computerised cognitive testing and volumetric brain MRI. Fighting history including years of fighting and fights per year was obtained from self-report and published records. Statistical analyses of the baseline evaluations were applied cross-sectionally to determine the relationship between fight exposure variables and volumes of the hippocampus, amygdala, thalamus, caudate, putamen. Moreover, the relationship between exposure and brain volumes with cognitive function was assessed.

Results: Increasing exposure to repetitive head trauma measured by number of professional fights, years of fighting, or a Fight Exposure Score (FES) was associated with lower brain volumes, particularly the thalamus and caudate. In addition, speed of processing decreased with decreased thalamic volumes and with increasing fight exposure. Higher scores on a FES used to reflect exposure to repetitive head trauma were associated with greater likelihood of having cognitive impairment.

Conclusions: Greater exposure to repetitive head trauma is associated with lower brain volumes and lower processing speed in active professional fighters.

Keywords: Boxing/Kick Boxing; Concussion; Contact sports; Epidemiology; Neurology.

Figure 1

Illustration of association between thalamus volume and the number of professional fights for boxers and mixed martial arts (MMA) fighters. The estimated mean volumes are standardised relative to a MMA fighter with zero professional fights.

Figure 2

Association between brain volume (in one-unit SD increments below and above the mean) and processing speed scores. Scores decrease 2–3% per one SD decrease in brain volume.

Figure 3

Illustration of the proportion of impaired fighters for the four cognitive domains as a function of the Fight Exposure Score (FES). Values above bars indicate the number of impaired participants with the given FES. There were 49 participants with a FES of 0, 114 participants with scores of 1 or 2 and 11 participants with scores of 3 or 4.