Thirty years after a truck bomb detonated outside a federal building in the nation’s heartland, deep scars still remain from the deadliest homegrown attack on U.S. soil.

Psychological trauma can unfortunately linger for years. However, according to recent research, it may even remain in the bodies of medically healthy people. The study, believed to be the first of its kind, was published in Prehospital and Disaster Medicine by a team at Oklahoma State University (OSU).