Traumatic brain injury (TBI) results from an impact to the head that disrupts normal brain functioning. The leading causes of TBI that resulted in emergency department visits are falls, being struck by an object and motor vehicle accidents. Indirect forces that jolt the brain violently within the skull (such as shock waves from battlefield or bomb explosions) can also cause TBI. In addition, bullet wounds or other injuries that penetrate the skull and brain typically cause TBI.
A traumatic brain injury's direct effects — which may be long-lasting or even permanent — can include unconsciousness, inability to recall the traumatic event, confusion, difficulty learning and remembering new information, trouble speaking coherently, unsteadiness, lack of coordination and problems with vision or hearing.
Even less severe TBI can affect a person’s cognitive abilities, including learning and thinking skills. In particular, Australian findings have shown a significant difference between the brains of former rugby players and men of a similar age with no history of concussion. (This research follows up on similar research that has been undertaken in the USA with American football players.) Furthermore, research that we have conducted ourselves produced evidence of some cognitive decline over a 3-year period in people over the aged of 60 who carried a specific genetic marker and who had previously sustained a head injury.
More generally, over the past 30 years international research has linked moderate and severe traumatic brain injury to a greater risk of developing Alzheimer's disease or another type of dementia years after the original head injury.