A TBI, or traumatic brain injury, refers to any injury that affects the functioning of the brain. A TBI usually occurs due to a violent blow or jolt to the head or body or due to an object piercing the skull into brain tissue, although some TBIs occur due to disease or infection or due to a lack of blood or oxygen flow to the brain. Mild TBIs only affect the brain temporarily, usually for a few minutes to a few days, while more serious injuries can result in permanent physical damage to brain tissue and lead to long-term complications or disabilities or even death.