War and other traumas give doctors great opportunities to study brain damage.
The brain seems remarkably plastic – parts that are injured often have their duties taken over by other parts, or the duties of those other parts are enhanced – sometimes remarkably.
The brain seems to be a highly redundant system – parts can drop out and the whole continues, often with little loss in fuction.
Large-scale attacks, like Alzheimer’s, seem to destroy or shut down large areas,
and there, even redundancy doesn’t help.
There are a few remarkable recent cases (and one well-known historical case).
In 1848, a 25-year-old railroad crew foreman named Phineas Gage and his crew were drilling blasting holes in rock. They were using a tamping iron to pack the blasting powder in a hole, when a spark set off the powder, sending the iron (3′ 8″ long, 1.25″ diameter at one end) through Gage’s head, entering under a cheekbone, exiting through the top of his head. (The iron was found some 30 yards away.)
Thanks to the miracle of then-modern medicine, he survived, and about four months later, apparently resumed a normal life.
Unfortunately, his personality changed, from “the most efficient and capable foreman”, to “a complete loss of social inhibitions”. That was attributed to the complete loss of his frontal cortex.
After he recovered, he wasn’t able to hold down a regular job, so he toured the country, with the tamping iron, raising a little money here and there. There is a photo of him with the iron. It’s almost unbelievable that he even survived.
His skull and the iron rod are now at the Harvard University School of Medicine.
The Gage case was one of the forerunners of research into localizing various functions – language, motor control, &c. – to areas of the brain.