Gross to you, gross to me

Last week a region of the brain called the insula was in the news. As I described in my post, scientists found that physical pain and social rejection both activate the insula in much the same way. The insula returns now for a disgusting encore that gives a glimpse at how we get inside other people’s heads.

European scientists had people sniff vials that gave off different odors while they were being scanned with MRI. Disgusting smells triggered a distinct constellation of neurons in the insula. Then the researcers showed the subjects videos of people smelling vials of their own. In some cases, the people in the videos either smiled with pleasure, showed no reaction, or screw up their face in disgust. When the subjects watched people being grossed out, the pattern of brain activation looked much the same in their insula and elswhere when they were being grossed out themselves. (The happy and neutral faces did produce this distinctive overlap.)

In the new issue of Neuron, the researchers propose that we perceive disgust in other people by using much of the same circuitry that produces our own feeling of disgust. Empathy, in other words, is not a purely intellectual exercise, but an immediate visceral response–at least when it comes to disgust. This reaction is probably an ancient response. Our primate ancestors 50 million years ago would have benefited from a quick response to nasty-tasting food. It’s possible that a visceral response to the sight of another primate eating some nasty-tasting food was helpful too–“Note to self: stay away from that fruit tree. It looks good, but Fred didn’t like it one bit.”

This week’s report adds to a growing collection of studies (like this one) now showing that we perceive other people through a sort of empathetic simulation. When we feel sympathy to someone in a sad situation, for example, a network of regions becomes active is responsible for forming mental images of actions we plan to take ourselves. Other mammals–particularly other primates–share some of this in-my-shoes circuitry, but in humans it has gotten extraordinarily elaborate. Only humans, for example, have a theory of mind, which lets us figure out not only that someone else is smelling something foul, but has foul plans for us. I wrote about this earlier this year in Science, pointing out that how our unique theory of mind may have been an essential ingredient for full-blown language.

From such disgusting beginnings…