Considerable human misery turns out to be attributable to an obscure corner of the brain, the insula.
In most mammalian brains, the insula’s function is straightforward. If a rat, say, bites into rancid food, its insula protects it from being poisoned by triggering nausea and gagging. In humans, however, the insula is not merely about gustatory disgust. If someone recounts something “rotten” they once did, or hears about someone else’s similar behavior, their insula activates. In other words, the insula also processes moral disgust. For example, if someone backstabs you in a game, the magnitude of your insula’s activation predicts how outraged you’ll feel, and how vengeful you’ll act. Our insula responds mainly to the disgustingness of sentient, intentional harm—if the person stabbed in the back believes a computer was to blame, her insula remains quiet. And if we’re sufficiently morally disgusted, ...
