Short answers, pulled from the story.
A brain injury, also known as brain damage or neurotrauma, is the destruction or degeneration of brain cells. It can result from external trauma such as accidents or falls, or from internal factors such as strokes, infections or metabolic disorders. Traumatic brain injury, the most common type, is typically caused by external physical trauma to the head.
Focal brain injuries affect a single area of the brain from direct force and appear as haemorrhages, contusions and haematomas, while diffuse injuries cause widespread damage from causes like diffuse axonal injuries and hypoxia. When both are severe, focal injuries are deadlier, with mortality rates of 40% against 25% for diffuse injuries. Diffuse injuries more often cause long-term neurological and cognitive deficits.
The Glasgow Coma Scale measures brain injury severity using eye opening worth 4 points, speech worth 5 points and motor ability worth 6 points. Severe brain injuries score 3 to 8, moderate injuries score 9 to 12, and mild injuries score 13 to 15. It is the most widely used scoring system for assessing brain injury severity.
Phineas Gage was a railroad construction foreman who in 1848 survived a tamping iron driven through his frontal lobe by an explosion. He kept his functional abilities but reportedly became rude, inconsiderate and indecisive, where his physician John Martyn Harlow said he had previously been friendly and respectful. Neuroscientist Malcolm Macmillan called it the most famous case of personality change after brain damage.
The brain can partially recover from injury through neuroplasticity, forming new neural connections to compensate for damaged areas. Patients may regain skills such as movement and speech, especially with therapy and practice. Full return to pre-injury cognitive function is not guaranteed but is not impossible, though neuroregeneration is far rarer in the central nervous system than the peripheral nervous system.
An average of 1,691,481 people, or 576.8 per 100,000, were hospitalised in the United States for traumatic brain injuries each year between 2002 and 2006. Of these, 51,538 died and 275,146 were hospitalised but survived. Between 70% and 95% of traumatic brain injuries are mild, and they occur more often and more severely in males than in females across all age groups.