Converging research has shown that subconcussive head impacts are a substantial source of acute and chronic structural and functional changes in the brains of contact sport athletes. Subconcussive head impacts involve the transmission of mechanical energy to the head from a force sufficient to cause neuronal injury or dysfunction, but they do not result in immediate overt clinical symptoms. From high school through professional play, athletes playing contact sports can experience hundreds of unrecognized subconcussive impacts in a single season, through which they continue to play, seemingly unharmed. Although large prospective studies are needed to understand this phenomenon, the frequency of subconcussive head impacts has been correlated with acute microstructural changes in cortical and deep gray matter structures of the brain, as well as impairments on neuropsychological testing in various samples of athletes playing contact sports, including football, soccer, and ice hockey.1 Growing evidence, primarily in former football players, further suggests that repetitive exposure to subconcussive impacts can lead to long-term neurobehavioral disturbances,2 including those from the neurodegenerative disease chronic traumatic encephalopathy (CTE).3,4 Recent experimental models of unilateral impact injuries that replicate subconcussive hits, not concussions, are associated with neuropathological changes resembling CTE in the brains of wild-type mice, including a progressive spread of focal tau accumulation to bilateral, widespread brain involvement.5 Given that millions of individuals play contact sports each year, it is paramount that we understand the associated risks of subconcussive head impacts.
McKee AC, Alosco ML. Assessing Subconcussive Head Impacts in Athletes Playing Contact Sports—The Eyes Have It. JAMA Ophthalmol. Published online December 20, 2018. doi:10.1001/jamaophthalmol.2018.6199
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