Chimpanzees sometimes smile from pleasure, as when baby chimps play with each other. But chimpanzees also smile when they’re trying to strengthen a social bond with another chimpanzee.Now here's something we're better at:
Dr. Niedenthal thinks that some human smiles fall into these categories as well. What’s more, they may be distinguished by certain expressions. An embarrassed smile is often accompanied by a lowered chin, for example, while a smile of greeting often comes with raised eyebrows.
Chimpanzees sometimes smile not for pleasure or for a social bond, but for power. A dominant chimpanzee will grin and show its teeth. Dr. Niedenthal argues that humans flash a power grin as well — often raising their chin so as to look down at others.
“ ‘You’re an idiot, I’m better than you’—that’s what we mean by a dominant smile,”
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. In their new paper, Dr. Niedenthal and her colleagues point to a number of studies indicating that this imitation activates many of the same regions of the brain that are active in the smiler.
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. It activates a region of the brain called the orbitofrontal cortex, which distinguishes feelings for people with whom we have a close relationship from others. The orbitofrontal cortex becomes active when parents see their own babies smile, for example, but not other babies.
If Dr. Niedenthal’s model is correct, then studies of dominant smiles should reveal different patterns of brain activity. Certain regions associated with negative emotions should become active.
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.