Repetitive head impacts, brain imaging, CTE pathology and TES research
Imaging and cognitive studies of professional fighters, the pathology of chronic traumatic encephalopathy (CTE), and research criteria for traumatic encephalopathy syndrome (TES).
Research information, not medical advice. This page does not diagnose, screen or clear anyone to compete.
Two terms need separating. In the pathology sources on this page, CTE was identified by examining brain tissue after death. TES has been proposed as the clinical presentation of suspected CTE in a living person, given current limits on diagnosing CTE clinically (Conway Kleven and colleagues, 2023).
Several of the imaging studies below draw on the same group of fighters, the Professional Fighters Brain Health Study. They are separate analyses of one cohort, not independent samples.
What the sources report
Repeated head trauma, thalamic volume and processing speed
Bernick et al., 2015. British Journal of Sports Medicine.
- Article type
- Cross-sectional baseline analysis
- Studied
- 224 professional fighters and 22 controls.
- Status
- Published in a peer-reviewed journal
- The analysis used baseline data from 224 professional fighters (131 MMA fighters and 93 boxers) and 22 controls in the Professional Fighters Brain Health Study.
- More fight exposure, measured by number of professional fights, years of fighting or a fight exposure score, was associated with lower brain volumes, most clearly in the thalamus and caudate.
- Processing speed was slower with smaller thalamic volume and with greater fight exposure.
Regional brain volumes over time with repetitive head impacts
Bernick et al., 2020. Neurology.
- Article type
- Longitudinal cohort analysis
- Studied
- 204 participants with repeated assessments, including fighters and controls.
- Status
- Published in a peer-reviewed journal
- 204 participants with at least two assessments were analysed.
- Compared with controls, active boxers showed a faster yearly decline in the volume of the left thalamus and parts of the corpus callosum. Retired boxers showed the largest declines in the amygdala and right hippocampus.
- Higher baseline neurofilament light levels were associated with greater volume decline in the left hippocampus and mid anterior corpus callosum.
Cognition and brain structure after fighters stop fighting
Zhuang et al., 2022. Neurology.
- Article type
- Longitudinal matched cohort analysis
- Studied
- 45 fighters who stopped fighting and sparring; 45 matched active fighters.
- Status
- Published in a peer-reviewed journal
- 45 male fighters who had no sanctioned fights and no sparring for two years were compared with 45 matched male fighters who stayed active.
- The two groups followed different paths in verbal memory, psychomotor speed, processing speed and neurofilament light levels. Fighters who stopped showed improved cognitive scores and falling neurofilament light. Active fighters showed declining cognitive scores.
- Cortical thickness measures stabilised at group level in the fighters who stopped and declined slightly in those who stayed active.
Weight class, brain volume and cognition in professional fighters
Bray et al., 2021. Neurotrauma Reports.
- Article type
- Analysis of a longitudinal cohort of professional fighters
- Studied
- 53 professional boxers and 103 professional MMA fighters enrolled in the Professional Fighters Brain Health Study.
- Status
- Published in a peer-reviewed journal
- Fighters had brain MRI scans and cognitive testing, and completed questionnaires on depressive symptoms, impulsivity and daytime sleepiness. The authors grouped them as lightweight (139.9 lb and under), middleweight (140.0 to 178.5 lb) or heavyweight (over 178.5 lb).
- Compared with lightweights, heavyweights showed larger yearly reductions in the volume of some deep brain structures and in some measures of thinking speed. The structures and tests differed between boxers and MMA fighters.
- Lightweights showed larger reductions in some of those structures per professional fight. The authors raise weight cutting as one possible explanation and say it needs more research.
Win-loss record, neuropsychiatric symptoms and brain health
Bryant et al., 2024. The Journal of Neuropsychiatry and Clinical Neurosciences.
- Article type
- Observational professional-fighter cohort analysis
- Studied
- 212 professional fighters.
- Status
- Published in a peer-reviewed journal
- Data from 212 professional fighters in the Professional Fighters Brain Health Study were analysed.
- Among retired fighters, a better win-loss record was associated with more impulsiveness, slower processing speed and smaller volumes in several brain regions.
- Fighters with better records did not score better than fighters with worse records on any neuropsychiatric or cognitive test.
Traumatic encephalopathy syndrome criteria in a fighter cohort
Ritter et al., 2023. British Journal of Sports Medicine.
- Article type
- Observational cohort analysis
- Studied
- 176 professional fighters: 110 boxers and 66 mixed martial artists.
- Status
- Published in a peer-reviewed journal
- Of 176 professional fighters who were 35 or older or retired (110 boxers and 66 MMA fighters), 72 (41%) met the NINDS consensus criteria for traumatic encephalopathy syndrome.
- The group meeting the criteria had lower regional brain volumes and lower scores on reaction time, psychomotor speed and Trails A.
- Fighters meeting the criteria tended to be boxers, to have started fighting younger, to have had more professional fights and to have been knocked out more often.
Brain volume and cognition over time in fighters with TES
Conway Kleven et al., 2023. Neurology.
- Article type
- Longitudinal secondary cohort analysis
- Studied
- 130 professional fighters aged 35 years and older.
- Status
- Published in a peer-reviewed journal
- Of 130 active and retired professional fighters older than 34, 52 (40%) were classified as meeting the 2021 traumatic encephalopathy syndrome criteria.
- Over time, the group meeting the criteria showed greater enlargement of the ventricles and greater loss of volume in the hippocampus, subcortical gray matter, total gray matter and posterior corpus callosum than the group that did not.
- Reaction time and other cognitive scores declined faster in the group meeting the criteria.
Head trauma in boxing: systematic review and meta-analysis
Donnelly et al., 2023. Clinical Journal of Sport Medicine.
- Article type
- Systematic review and meta-analysis
- Studied
- 35 included boxing studies.
- Status
- Published in a peer-reviewed journal
- 35 studies were included.
- The review reports a higher concussion risk in boxing than in other combat sports.
- Among boxers in the included studies, 147 of 631 had cavum septum pellucidum and 125 of 411 had some form of brain atrophy.
The aftermath of boxing revisited
Goldfinger et al., 2018. Acta Neuropathologica.
- Article type
- Archival neuropathology study, published as correspondence
- Studied
- Preserved brain tissue from 14 of the 15 boxers first described by Corsellis and colleagues in 1973.
- Status
- Published in a peer-reviewed journal
- The authors stained tissue from 14 of the original 15 cases for abnormal tau protein and judged each case against the preliminary consensus criteria for CTE published in 2016.
- Seven of the 14 cases met those criteria. One of the seven also showed Alzheimer’s disease pathology.
- Ten cases showed a separate age-related tau change in support cells of the brain, including all seven CTE cases. Two cases showed no abnormality, and the authors could not confirm a boxing history for those two.
CTE: features and forensic considerations
Byard et al., 2023. Forensic Science, Medicine and Pathology.
- Article type
- Commentary and pathology reference
- Studied
- Not a study of participants. Its scope is wider than combat sports: contact sport in general and other groups exposed to repeated head trauma.
- Status
- Published in a peer-reviewed journal
- The authors describe CTE as a degenerative brain condition and state that its only known cause is repeated blunt head trauma.
- They describe the finding that defines CTE under the microscope: abnormal tau protein in nerve cells around small blood vessels deep in the folds of the brain’s surface.
- They recommend that death investigations ask about past head trauma, including contact sport, and that the brain be examined and sampled so cases are not missed. They describe tau staining of three areas of the outer brain as a useful screen.
Psychiatric features of TES in 20th-century boxing cases
Iverson et al., 2023. Frontiers in Neurology.
- Article type
- Narrative review of historical clinical case descriptions
- Studied
- 155 current and former boxers described in 21 publications from 1928–1999.
- Status
- Published in a peer-reviewed journal
Scope: Historical case descriptions published between 1928 and 1999.
- The authors reviewed clinical descriptions of 155 current and former boxers from 21 articles published between 1928 and 1999.
- A psychiatric, neuropsychiatric or neurobehavioral problem was described in 34.8% of cases. 6.5% of cases were described as primarily psychiatric or neuropsychiatric.
- Depression was documented in 11.0% of cases, anxiety in 3.9% and suicidality in 0.6%. The authors conclude that these were not considered clinical features of the syndrome in the 20th-century literature.
Limits of this evidence
- Most of the imaging studies analyse one cohort. Agreement between them is not independent confirmation.
- These studies report patterns across groups of fighters. They do not predict what will happen to any one fighter.
- TES criteria are research criteria. The studies here test how the criteria behave in a cohort of fighters.
- The pathology sources describe findings in brain tissue and forensic practice. They do not estimate how common CTE is among fighters.
Fight Medicine Research Institute checked each source’s details against PubMed, Crossref, Europe PMC or the publisher. It has not carried out a formal critical appraisal of each paper.