A traumatic brain injury (TBI) is defined as brain dysfunction caused by an outside force, usually a violent blow to the head. In a report issued to Congress in March by the Centers for Disease Control and Prevention (CDC), it was estimated that in one year alone, TBIs accounted for approximately 2.2 million emergency department visits, 280,000 hospitalizations, and 50,000 deaths. Although a TBI begins with a physical trauma, it quickly leads to a series of chemical and structural changes in the brain — it can affect how a person feels, thinks, acts and learns long after medical treatment and rehabilitation are completed. The brain is a complicated organ, and there is no way of knowing how it will react in any given set of circumstances. Some injuries leave patients alive but unconscious or severely impaired. Others are seemingly mild, yet cause slight but continual changes in mood, memory, and cognitive abilities. So, it’s not hard to believe that TBIs could affect how people drive. Working with the knowledge that driver aggression and the risk of driving wrecks are strongly affected by psychiatric factors, researchers in Toronto, Canada, surveyed almost 4,000 adult drivers between the ages of 18 and 97. Conducted by the Centre for Addiction and Mental Health from 2011 to 2012 and published in the journal Accident Analysis and Prevention, the study was the first of its kind to examine the link between traumatic brain injuries and aggressive driving behaviors.