There has been increasing recognition of the long-term neurological complications that can occur in those exposed to repeated head trauma, not only athletes, but also in the civilian and military population. And given the numbers of people that participate in sports and the military, this is a far-reaching public health issue.

It has been known for decades that boxers are particularly susceptible to develop “punch drunk” syndrome (now called chronic traumatic encephalopathy or CTE), parkinsonism or dementia. An important gap in our knowledge of the consequences of cumulative head trauma is how these brain disorders evolve and how early can they be detected.

Cleveland Clinic Lou Ruvo Center for Brain Health has been involved in two major research initiatives regarding long term effects of repetitive head trauma. The Diagnose CTE study, involving retired National Football League players, and the Professional Athletes Brain Health study are both focused on determining methods to recognize/diagnose individuals who may have CTE and identifying potential risk factors.

Closing the Gap

Since the first participant was enrolled in 2011, Cleveland Clinic’s Professional Fighters Brain Health Study — now known as the Professional Athletes Brain Health Study (PABHS) — has become a landmark longitudinal, observational study of athletes exposed to repeated head impacts (RHI) and the first to study retired and active men and women professional athletes concurrently.

PABHS is aimed at understanding the long-term effects of RHI, including means to detect accumulating brain injury early and factors that put certain individuals at higher risk — or protect them from — developing CTE.

PABHS researchers continue to diversify the cohort of athletes to include more women, retired athletes and bull riders, as well as recruit additional athletes from other sports, such as hockey and motor sports.

More than a decade later, researchers have made several advancements in our knowledge of CTE, including:

  • Development of new research criteria for Traumatic Encephalopathy Syndrome (TES) that will allow us to diagnose living people with symptoms that are suggestive of CTE (though CTE remains diagnosable only via autopsy).
  • Establishing the pathological hallmarks of disease — aggregates of tau around blood vessels deep within the folds of the brain.

Other notable findings from this research include:

  • Subtle effects of RHI on brain structure can be seen in some athletes within a year and can be tracked over time. The areas that we see change differ between people who are actively exposed to RHI compared to those who are retired and no longer exposed. This finding implies that there may be different pathological processes occurring in the brain in those who are active and those who have retired.
  • Certain proteins that are indicators of inflammation and cellular damage can leak out of the brain and can be measured in the blood. One particular protein, glial fibrillary acidic protein or GFAP, may be useful in detecting ongoing brain injury.
  • Individuals who began the study actively competing in combat sports and who then retire can show improvement or stabilization in both biochemical and clinical measures of brain function, suggesting the brain has the potential to repair.
  • The Repetitive Head Impact Composite Index has been created as a tool that is sensitive to the common cognitive and behavioral changes seen in individuals exposed to RHI and may be used to monitor response to therapies as we begin clinical trials in CTE.
  • The risk of brain injury differs between various combat sports (e.g., MMA, boxing, martial arts) as measured by cognitive performance (memory, thinking and speed of completing cognitive activities) and certain brain volume.

Contact Information

Charles Bernick, MD, MPH



Examination of parkinsonism in former elite American football players. Alosco ML, Adler CH, Dodick DW, Tripodis Y, Balcer LJ, Bernick C, Banks SJ, et al. Parkinsonism Relat Disord. 2023 Nov 14:105903. Doi: 10.1016/j.parkreldis.2023.105903.

Blood biomarkers and neurodegeneration in individuals exposed to repetitive head impacts. Charles Bernick, Guogen Shan, Aaron Ritter, Nicolas J Ashton, Kaj Blennow, Juan Lantero-Rodriguez, Anniina Snellman, Henrik Zetterberg. Alzheimers Res Ther. 2023 Oct 12; 15(1):173. Doi 10.1186/s13195-023-01310-w

Amyloid PET across the cognitive spectrum in former professional and college American football players: findings from the Diagnose CTE Research Project. Robert A Stern, Diana Trujillo-Rodriguez, Yorghos Tripodis, Surya V Pulukuri, Michael L Alosco, Charles H Adler, Laura J Balcer, Charles Bernic et al. Alzheimers Res Ther. 2023 Oct 5;15(1):166. Doi: 10.1186/s13195-023-01315-5

Cocaine history and impulsiveness in professional boxers and mixed martial arts fighters. Lisa Young, Aaron Esagoff, Anne Reisch, Charles B Bernick, Matthew E Peters, Bharat R Narapareddy. Am J Addict. 2023 Sep 5. Doi: 10.1111/ajad.13479.

Longitudinal Changes in Regional Brain Volumes and Cognition of Professional Fighters With Traumatic Encephalopathy Syndrome. Conway Kleven BD, Chien LC, Labus B, Cross CL, Ritter A, Randall R, Montes A, Bernick C. Neurology. 2023 Jun 28;10.1212/WNL.0000000000207594. doi: 10.1212/WNL.0000000000207594.

7T MRI Versus 3T MRI of the Brain in Professional Fighters and Patients With Head Trauma. Lee JK, Bernick C, Stephen S, Ritter A, Bullen J, Mangat A, Joyce J, Jones SE.. Neurotrauma Rep. 2023 May 18;4(1):342-349.doi: 10.1089/neur.2023.0001

Sparring and the Brain: The Associations between Sparring and Regional Brain Volumes in Professional Mixed Martial Arts Fighters. Esagoff A.I., Heckenlaible N.J., Bray M.J.C., Bernick C et al. Sports Med. 2023 Mar 27. doi: 10.1007/s40279-023-01838-9.

Articulation Rate, Pauses, and Disfluencies in Professional Fighters: Potential Speech Biomarkers for Repetitive Head Injury. Neel A, Krasilshchikova S, Richardson J, Arenas R, Bennett L, Banks S, Ritter A, Bernick C. J Head Trauma Rehabil. 2023 Jan 26. doi: 10.1097/HTR.0000000000000841

Neuropsychological test performance of former American football players. Alosco M, Barr W, Banks S, Wethe J, Miller J, Pulukuri S, Culhane J, Tripodis Y, Adler C, Balcer L, Bernick C, et al. Alzheimer’s Res Ther. 2023 Jan 3. doi:10.1186/s13195-022-01147-9

Traumatic encephalopathy syndrome: application of new criteria to a cohort exposed to repetitive head impacts. Ritter A, Shan G, Montes A, Randall R, Bernick C. Br J Sports Med. 2022 Dec 14. doi:10.1136/bjsports-2022-105819

Associations between near end-of-life flortaucipir PET and postmortem CTE-related tau neuropathology in six former American football players. Alosco ML, Su Y, Stein TD, Protas H, Cherry JD, Adler CH, Balcer LJ, Bernick C, et al. Eur J Nucl Med Mol Imaging. 2022 Sep 24. doi: 10.1007/s00259-022-05963-x.

White matter hyperintensities in former American football players. Alosco ML, Tripodis Y, Baucom ZH, Adler CH, Balcer LJ, Bernick C, et al. Alzheimer’s Dement. 2022 Aug 22. doi: 10.1002/alz.12779.

Longitudinal changes in cognitive functioning and brain structure in professional boxers and mixed martial artists after they stop fighting. Zhuang, X, Bennett L, Nandy R, Cordes D, Bernick C, Ritter A. Neurology. 2022 Sep 14;99(20):e2275-e2284. doi:10.1212/WNL.0000000000201158.

Developing methods to detect and diagnose chronic traumatic encephalopathy during life: rationale, design, and methodology for the DIAGNOSE CTE Research Project. Alosco ML, Mariani ML, Adler CH, Balcer LJ, Bernick C, et al. Alzheimer’s Res Ther. 2021 Aug 12;13(1):136. doi: 10.1186/s13195-021-00872-x

Effect of Weight Class on Regional Brain Volume, Cognition, and Other Neuropsychiatric Outcomes among Professional Fighters. Bray MJC, Tsai J, Bryant BR, Narapareddy BR, Richey LN, Krieg A, Tobolowsky W, Jahed S, Shan G, Bernick CB, Peters ME. Neurotrauma Rep. 2021 Mar 18;2(1):169-179. doi: 10.1089/neur.2020.0057

Assessing Clinical Change in Individuals Exposed to Repetitive Head Impacts: The Repetitive Head Impact Composite Index. Bernick C, Shan G, Bennett L, Alberts J, Cummings J. Front Neurol. 2021 Jul 6;12:605318. doi:10.3389/fneur.2021.605318

National Institute of Neurological Disorders and Stroke Consensus Diagnostic Criteria for Traumatic Encephalopathy Syndrome. Katz DI, Bernick C, Dodick DW, et al. Neurology. 2021 May 4;96(18):848-863. doi:10.1212/WNL.0000000000011850.

The Relationship Between Fighting Style, Cognition, and Regional Brain Volume in Professional Combatants: A Preliminary Examination Using Brief Neurocognitive Measures. Stephen SJ, Shan G, Banks SJ, Bernick C, Bennett LL. Journal of Head Trauma Rehabilitation. 2020 May/Jun;35(3:E280-E287. doi:10.1097/HTR.0000000000000540

Resting-State Static and Dynamic Functional Abnormalities in Active Professional Fighters With Repetitive Head Trauma and With Neuropsychological Impairments. Zhuang X, Mishra V, Nandy R, Yang Z, Sreenivasan K, Bennett L, Bernick C, Cordes D. Front Neurol. 2020 Dec 10;11:602586. doi: 10.3389/fneur.2020.602586.

Concussion occurrence and recognition in professional boxing and MMA matches: toward a concussion protocol in combat sports. Bernick C, Hansen T, Ng W, Williams V, Goodman M, Nalepa B, Shan G, Seifert T. The Physician and Sportsmedicine. 2020 Dec 31;49:4, 469-475,doi:10.1080/00913847.2020.1856631.

Sex Moderates the Relationship That Number of Professional Fights Has With Cognition and Brain Volumes. Bennett LL, Stephen SJ, Bernick C, Shan G, Banks SJ. Front Neurol. 2020 Oct 29;11:574458. doi: 10.3389/fneur.2020.574458

History of Chronic Traumatic Encephalopathy. Cantu RC, Bernick C. Semin Neurol. 2020 Aug;40(4):353-358. doi: 10.1055/s-0040-1713622. Epub 2020 Aug 10

Longitudinal change in regional brain volumes with exposure to repetitive head impacts. Bernick C, Shan G, Zetterberg H, Banks S, Mishra VR, Bekris L, Leverenz JB, Blennow K. Neurology. 2020 Jan 21;94(3):e232-e240. doi: 10.1212/WNL.0000000000008817.

The effect of age of first exposure to competitive fighting on cognitive and other neuropsychiatric symptoms and brain volume. Bryant BR, Narapareddy BR, Bray MJC, Richey LN, Krieg A, Shan G, Peters ME, Bernick CB. Int Rev Psychiatry. 2019 Oct 7:1-7. doi: 10.1080/09540261.2019.1665501.

Association of Cavum Septum Pellucidum and Cavum Vergae With Cognition, Mood, and Brain Volumes in Professional Fighters. Lee JK, Wu J, Bullen J, Banks S, Bernick C, Modic MT, Ruggieri P, Bennett L, Jones SE. JAMA Neurol. 2019 Sep 9. doi: 10.1001/jamaneurol.2019.2861.

Understanding white matter structural connectivity differences between cognitively impaired and nonimpaired active professional fighters. Mishra VR, Sreenivasan KR, Zhuang X, Yang Z, Cordes D, Banks SJ, Bernick C. Hum Brain Mapp. 2019 Aug 12. doi: 10.1002/hbm.24761.

The relationship among depression, cognition and brain volume in professional boxers: A Preliminary Examination Using Brief Clinical Measures. Lee B, Bennett L, Bernick C, Shan G, Banks S.. Journal of Head Trauma Rehabil. 2019 Apr 25. doi: 10.1097/HTR.0000000000000495.

Members & Collaborations

Members & Collaborations

Cleveland Clinic Affiliations

  • Charles Bernick, MD, MPH
  • Aaron Ritter, MD

External Relationships and Collaborations

  • Boston University
  • Case Western Reserve University
  • Indiana University
  • Johns Hopkins
  • The Sahlgrenska Academy at University of Gothenburg
  • University of California, San Diego
  • University of Minnesota
  • University of New Mexico, Albuquerque
  • University of Washington, Seattle