a temporary loss of brain function resulting from a relatively mild injury to the brain, not necessarily associated with unconsciousness. Those with concussions may not remember what happened immediately before or after their injury. Symptoms of a concussion include slurred speech, confusion, impaired muscle coordination, headache, dizziness, and nausea. Professional medical care should be sought to rule out the possibility of bleeding or swelling of the brain.

Recovery from an uncomplicated concussion is almost always complete; however, sustaining multiple concussions or a moderate or severe concussion has been associated with long-lasting effects on the brain. Studies of retired athletes who sustained concussions in early adulthood have linked these injuries to reduced memory performance and bradykinesia (slowness of movement) in late life. Furthermore, there is some evidence indicating that severe concussion may be associated with the eventual onset of mild cognitive impairment and dementia.