Even mild concussions can 'rewire' the brain, possibly causing long-term symptoms

two soccer players, one in a red jersey and white shorts and one in a white jersey and black shorts, pass each other on the pitch, having just collided. The player in white holds his head in one hand as if in pain

Even light bumps on the head can cause long-term problems, and researchers may now have an idea why: The brain's wiring can change in the aftermath of mild concussions.   

Prior studies suggested that even mild traumatic brain injuries (TBI) that don't cause any observable structural damage can still trigger symptoms that persist for more than six months. These symptoms range from problems with concentration and fatigue to depression and anxiety.