Traumatic brain injury is when your head is basically struck in some fashion, or you make contact with an external object and it injures your brain. There is a Frenchmen who called this ecou contre ecou, when you shake your head, your brain goes the opposite way, and it can bang inside your head and literally injure your brain. That's traumatic brain injury. There's levels of severity, from people that are catatonic to people that have non-observable, but discernible and real problems.
