The Frontal Cortex

The New Yorker recently had a cool short story by T.C. Boyle about a boy who couldn't experience pain. The story is told from the perspective of a doctor who has trouble believing that the symptoms of the child are real. The mother pleads:

"He's not normal, doctor. He doesn't feel pain the way others do. Look here"--and she lifted the child's right leg as if it weren't even attached to him, rolling up his miniature trousers to show me a dark raised scar the size of an adult's spread hand--"do you see this? This is where that filthy pit bull Isabel Briceño keeps came through the fence and bit him, and we've gone to the lawyer over it, too, believe me, but he never cried out or said a word. The dog had him down in the dirt, chewing on him like he was a bone, and if my husband hadn't gone out into the yard to throw his shaving water on the rosebushes I think he would have been torn to pieces."

[snip]

"We call him Sin Dolor, doctor. That's his nickname. That's what his father calls him when he misbehaves, because no amount of spanking or pinching or twisting his arm will even begin to touch him. Sin Dolor, doctor. The Painless One."

From the perspective of the brain, there are two distinct types of pain. The first type of pain is sensory. When we stub our toe, pain receptors in the foot instantly react to the injury, and send an angry message to the somatosensory cortex, the part of the brain that deals with the body. The hurt has a clear bodily cause: if you inject an anesthetic (like novocaine) into the stubbed toe, the pain will quickly disappear. Rare genetic conditions can leave people unable to experience any pain at all. Like the boy in the short story, they are at constant risk of injury.

The second pain pathway is a much more recent scientific discovery. It runs parallel to the sensory pathway, but isn't necessarily rooted in signals from the body. The breakthrough came when neurologists discovered a group of people who, after a brain injury, were no longer bothered by pain. They still felt the pain, and could accurately describe its location and intensity, but didn't seem to mind it at all. The agony wasn't agonizing.

This strange condition - it's known as pain asymbolia - results from damage to a specific subset of brain areas, like the amygdala, insula and anterior cingulate cortex, that are involved in the processing of emotions. As a result, these people are missing the negative feelings that normally accompany our painful sensations. Their muted response to bodily injury demonstrates that it is our feelings about pain - and not the pain sensation itself - that make the experience of pain so awful. Take away the emotion and a stubbed toe isn't so bad.

It's never quite clear what causes the boy's disease of painlessness in the short story - a "mutation" is vaguely referenced - but such diseases are all too real.

Update: Check out p-ter's post on this short story. T.C. Boyle, it turns out, reads Nature.