The progressive cognitive and behavioural symptoms in CTE are the result of a complex, chronic inflammatory process, which leads to destruction of the normal connections between the brain cells and death of the brain cells.
With repetitive impacts to the head the most significant injury occurs to the tiny blood vessels in the brain. This in turn results in damage to the ‘blood brain’ barrier, a structure designed to protect the brain.
When this structure is damaged by repetitive trauma, an abnormal ‘immune” mediated inflammatory response is triggered, with the production of neurochemicals. The neurochemicals and inflammatory response, should be protective.
However, when the brain is subjected to repetitive blows and before the protective neurochemicals and inflammatory changes from the initial brain injury have had time to return to normal, the subsequent, repetitive head injuries can then result in an abnormally exaggerated further production of neurochemicals and an exaggerated inflammatory response. This is harmful to the brain, instead of protective. The response now damages the brain tissue and eventually leads to the irreversible death of brain cells.
Over time, this abnormal inflammatory pathway which is triggered, repeatedly, by frequent head injury in contact sports eventually leads to changes in a brain protein called tau.
The tau protein which is found within cognitive brain cells normally stabilises these brain cells to ensure they work efficiently and communicate effectively, with all the other cognitive brain cells, so an individual can think and behave normally.
When the tau protein becomes damaged, it can no longer stabilise the brain cells and the brain cells lose their ability to function efficiently and effectively.
Furthermore, the tau protein starts to replicate itself inside the brain cells and eventually the tau completely fills the brain cells so they burst and die. Unfortunately, these brain cells cannot regenerate. The abnormal tau protein also develops the ability to “jump” from one brain cell to the next; once the abnormal tau protein enters a new brain cell, the process starts again, resulting in the death of that brain cell.
As the tau protein spreads around the brain affecting and killing more and more brain cells, needed for thinking and to control our emotions and behaviour, the symptoms of cognitive impairment and changes in behaviour become increasingly apparent. The resulting symptoms result in CTE.