Traumatic brain injuries (TBI), also known as concussions, are impacts to the head that interrupt the normal function of the brain. Concussion is the most common but least serious type of brain injury. It is estimated that one in every 2,000 people will experience an episode of concussion requiring hospital treatment each year. However, the actual figure could be much higher, as many people do not seek treatment for concussion. Researchers from the World Health Organization estimated that the true number of people affected by concussion each year could be as high as one in 165.