History of biological, mechanistic, and clinical understanding of concussion.

The history behind the biological, mechanistic, and clinical insights into concussion provides awareness of the current understanding and future areas for study. Although the initial description of concussion appeared in the 10th century, the potential long-term structural consequences were first defined by Harrison Martland, M.D., who performed a postmortem study of former boxers in 1928. He found evidence of perivascular microhemorrhage that he believed eventually evolved into a "replacement gliosis" underlying a clinical syndrome that he named "punch drunk," which was characterized by acute confusion with chronic cognitive and physical symptoms developing in those with prolonged exposure. Further research into the potential long-term consequences of repetitive concussions, particularly in athletics and the military, led to an understanding of chronic traumatic encephalopathy. To ameliorate possible long-term risks, research has been focused on preventative and therapeutic measures for concussion. In this review article, the authors present the history of concussion and the long-term sequelae of repeated head injury. Specifically, they consider how the understanding of concussion has evolved from antiquity into the modern era, and how this change in understanding of head injury has led to an appreciation of the fact that its long-term implications sometimes manifest as the clinical and histopathological entity of chronic traumatic encephalopathy.