A very interesting new study on smiles, which nicely illustrates the connection between emotion, cognition, and embodiment.

Paula Niedenthal… and her colleagues have surveyed a wide range of studies, from brain scans to cultural observations, to build a new scientific model of the smile. They believe they can account not only for the source of smiles, but how people perceive them. In a recent issue of the journal Behavioral and Brain Sciences, they argue that smiles are not simply the expression of an internal feeling. Smiles in fact are only the most visible part of an intimate melding between two minds.

One of the things her team has analyzed is how people recognize smiles.

One way people recognize smiles is comparing the geometry of a person’s face to a standard smile. A second way is thinking about the situation in which someone is making an expression, judging if it’s the sort where a smile would be expected.

But most importantly, Dr. Niedenthal argues, people recognize smiles by mimicking them. When a smiling person locks eyes with another person, the viewer unknowingly mimics a smile as well…. A happy smile, for example, is accompanied by activity in the brain’s reward circuits, and looking at a happy smile can excite those circuits as well. Mimicking a friendly smile produces a different pattern of brain activity…. Embodying smiles not only lets people recognize smiles, Dr. Niedenthal argues. It also lets them recognize false smiles. When they unconsciously mimic a false smile, they don’t experience the same brain activity as an authentic one. The mismatch lets them know something’s wrong.

So one of the ways we recognize a smile is to mimic it, and to evaluate its veracity based on how that mimicry feels.

One compelling piece of evidence for the importance of this evaluation tool is that you can short-circuit this system by freezing the facial muscles of the person who’s looking at a smile:

In one study, she and her colleagues are testing the idea that mimicry lets people recognize authentic smiles. They showed pictures of smiling people to a group of students. Some of the smiles were genuine and others were fake. The students could readily tell the difference between them.

Then Dr. Niedenthal and her colleagues asked the students to place a pencil between their lips. This simple action engaged muscles that could otherwise produce a smile. Unable to mimic the faces they saw, the students had a much harder time telling which smiles were real and which were fake.