A common way that a person can experience a traumatic brain injury is when an impact or violent motion brings their head to a sudden stop, causing the brain to slam into the skull. This is called a coup-contrecoup injury, also known as an acceleration / deceleration injury.
In this kind of injury, the brain bounces back and forth inside of the head, causing damage to the brain where it hits the skull. The brain is injured at the point of direct impact, and because it bounces back into the opposite side of the skull, the opposite side of the brain is injured as well.
Coup-contrecoup injuries can involve damage to the brain at the specific point of impact, called focal injuries, or to a large part of the brain, known as diffuse injuries.
It’s important to know that coup-contrecoup injuries can happen as the result of trauma without direct impact to the head, since it is the movement of the brain inside of the skull that causes the injury.