History
The Hippocratic Corpus, a collection of medical works from ancient Greece, mentions concussion, later translated to commotio cerebri, and discusses loss of speech, hearing and sight that can result from "commotion of the brain". This idea of disruption of mental function by "shaking of the brain" remained the widely accepted understanding of concussion until the 19th century. In the 10th century, the Persian physician Muhammad ibn Zakarīya Rāzi was the first to write about concussion as distinct from other types of head injury. He may have been the first to use the term "cerebral concussion", and his definition of the condition, a transient loss of function with no physical damage, set the stage for the medical understanding of the condition for centuries.In the 13th century, the physician Lanfranc of Milans Chiurgia Magna described concussion as brain "commotion", also recognizing a difference between concussion and other types of traumatic brain injury (though many of his contemporaries did not), and discussing the transience of post-concussion symptoms as a result of temporary loss of function from the injury. In the 14th century, the surgeon Guy de Chauliac pointed out the relatively good prognosis of concussion as compared to more severe types of head trauma such as skull fractures and penetrating head trauma. In the 16th-century, the term "concussion" came into use, and symptoms such as confusion, lethargy, and memory problems were described. The 16th century physician Ambroise Paré used the term commotio cerebri, as well as "shaking of the brain", "commotion", and "concussion".
According to studies performed on animals (which are not always applicable to humans), large numbers of neurons can die during this period in response to slight, normally innocuous changes in blood flow.Concussion involves diffuse (as opposed to focal) brain injury, meaning that the dysfunction occurs over a widespread area of the brain rather than in a particular spot. It is thought to be a milder type of diffuse axonal injury, because axons may be injured to a minor extent due to stretching. Animal studies in which rodents were concussed have revealed lifelong neuropathological consequences such as ongoing axonal degeneration and neuroinflammation in subcortical white matter tracts. Axonal damage has been found in the brains of concussion patients who died from other causes, but inadequate blood flow to the brain due to other injuries may have contributed. Findings from a study of the brains of deceased NFL athletes who received concussions suggest that lasting damage is done by such injuries. This damage, the severity of which increases with the cumulative number of concussions sustained, can lead to a variety of other health issues.The debate over whether concussion is a functional or structural phenomenon is ongoing. Structural damage has been found in the mildly traumatically injured brains of animals, but it is not clear whether these findings would apply to humans.