Measures of the integrity of midbrain white matter in 38 college-level American football players changed after a season of play even though all but two of the athletes did not suffer clinically defined concussions, according to a new study. The results indicate that repeated, subconcussive head hits sustained by players over the course of a typical football game can cumulatively cause brain trauma. The authors say this suggests that catching injury before it manifests as overt signs and symptoms will prove critical in protecting players from long-term neurologic injury. Although the buildup of tau protein in the midbrain is already associated with neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), it has not been definitively known whether structural changes to the midbrain occur during the repetitive head impacts that fall short of the clinical diagnosis for concussion. Adnan Hirad et al. examined the midbrain white matter of players before and after a college football season using an MRI-based imaging technique. They also measured the magnitude, location, and direction of hits experienced on the field with accelerometers attached to the players' helmets. The researchers found that the degree of reduction in midbrain white matter structural integrity was linked to the number of impacts that caused the brain to rotate inside the skull (while impacts that caused the brain to strike the front or rear of the skull were not). Further MRI analysis of white matter structural integrity in a second cohort of 29 patients with clinically defined concussions compared to 58 controls of the same age suggested that changes in the midbrain regions of the concussed group were related to tau accumulation. "The midbrain may be the place to look," the authors sayin a related video, "to predict the injury burden of contact sports in the absence of concussion."