In this new study, Bellgowan and his colleagues used MRI, or magnetic resonance imaging, to scan the brains of participants. The technique allowed them to measure the hippocampus in 50 college football players. About half the football players had been diagnosed with a concussion in the past. The researchers did the same in 25 male volunteers of the same age. The volunteers hadn’t played football or soccer. (Concussions occur among players of both sports.)