Lay summary – Traumatic brain injury and repeated head impacts may increase the risk of later-life brain changes, including CTE. This study examined donated brain tissue from people with a history of TBI or contact sports participation and compared it with tissue from people without known injury. The researchers found that a type of abnormal tau build-up in brain support cells was more common after repeated head impacts or TBI, and appeared in particular areas of the brain. The findings suggest that head trauma may be linked to wider brain changes beyond CTE, but more research is needed to understand what these changes mean for symptoms and long-term health.