Thou can’t not covet

As every kid knows, the very best toy is the one that someone else is playing with. A new study on covetous adults explains why other people’s possessions always seem better.

Seeds of this desire are sown in the mirror neuron system, a part of the brain that is activated in a similar pattern whether a person is performing an action or merely watching someone else do it.

“Mimetic desire” was first articulated by the French philosopher René Girard in the 1980s. Envy can spread among people like a disease, a force that explains much of human behavior, Girard proposed. Now, French neuroscientists have verified the phenomenon and even attempted to explain how it happens.

“They really take a philosophical theory and make it an experiment,” says neuroscientist Marco Iacoboni of UCLA.

Copying other people’s desires is a good way to learn about the environment, says study coauthor Mathias Pessiglione of INSERM in Paris. Eating the food that other people eat, for example, is a simple way to avoid food poisoning. But this adaptive feature can break down when desired objects are in short supply.

Pessiglione and his team showed adults one of two videos: a piece of candy sitting on a surface, or a person’s hand reaching toward a different-colored piece of candy. Participants then rated the desirability of each candy they saw. As the mimetic desire theory predicts, people rated the about-to-get-grabbed candy as more desirable. The same effect held for clothes, tools and even toys, the team reports in the May 23 Journal of Neuroscience.

Brain scans revealed that two systems are behind the phenomenon. First, activity in parts of the brain’s mirror neuron system — the parietal lobe and the premotor cortex — increased. Second, the parts of the brain involved with deciding how much objects are worth — the ventral striatum and the ventromedial prefrontal cortex — got busy.

These two systems are linked, so that the mirror neuron system kicks on and tells the brain’s valuation system to rank the object highly, the team’s analyses of the brain scans revealed. 

The strength of this connection was associated with how much mimetic desire a person felt, the team found. A stronger connection meant a deeper longing for someone else’s candy. “The stronger the connection, the more susceptible you are to social influence,” Pessiglione says.

These results raise lots of questions that can now be tested, Iacoboni says. “This could start a whole snowball effect.” Similar experiments could test whether people with autism spectrum disorders, who seem to value social interactions less, have a weaker connection between the mirror neuron system and the brain valuation system.

Other experiments might test the limits of mimetic desire by replacing an obviously human hand with a robot’s or a chimp’s.