Why smiles and frowns are contagious

Extracting the emotional state of a person in front of you from a split-second facial twitch sounds far-fetched, but it's a leading theory in social psychology. Belinda Smith reports.

A toothy grin might not elicit giant smiles from others, but it should prompt an unconscious twitch. – Lisa Barnes / Getty Images

When you're smiling, the whole world smiles with you ... well, the people watching your face do, even if it's an unconscious twitch over in a fraction of a second.

Contagious smiling (and frowning and scowling and so on) is the basis of reading others' emotions and registering how you should, in turn, feel. Contrary to logic, when you meet someone face-to-face, you don't consciously process their expression, register a happy smile, and then smile back.

Instead, you mimic their expression unconsciously, which then tells your brain what to feel. All this happens in a few hundred milliseconds.

The part of the brain responsible for mirroring is called the inferior frontal gyrus, which sits above your temple towards the forehead.

This "emotional mirroring" is one theory of emotional perception and the subject of much psychological research. And, like all body systems, things can go awry.

A pair of US psychologists in 2011 found people who used botox, a popular anti-wrinkle treatment that freezes muscles, were less able to judge others' emotions compared to subjects who only used dermal fillers (which plump the skin rather than freeze it).

Why? When presented with a facial expression, their frozen muscles were unable to unconsciously mimic it. This interrupted emotional information to the brain.

Magnetic pulses to the brain can "switch off" specific areas. When scientists applied transcranical magnetic stimulation to the primary motor cortex, which is responsible for planning and executing movement, they found subjects were less able to recognise emotions than if they zapped the somatosensory cortex, which processes touch, temperature and pain.

And a 2012 study found boys who used pacifiers longest had reduced "emotional competence" compared to those who dropped the dummy, and were able to better mimic faces, earlier.

When given questionnaires as young adults, boys who spent more time sucking on a pacifier had lower emotional intelligence.

The same effect wasn't seen in girls. The researchers pinned this on parents talking to girls more about emotions.

There are, of course, other theories for emotional recognition in faces. People with Moebius syndrome, bi-lateral facial paralysis, can perceive emotions, even though they're unable to mimic them.

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  1. http://www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(16)00016-4
  2. http://spp.sagepub.com/content/2/6/673.short
  3. http://www.sciencedirect.com/science/article/pii/S0028393208001905
  4. http://www.tandfonline.com/doi/abs/10.1080/01973533.2012.712019
  5. http://www.tandfonline.com/doi/abs/10.1080/17470910903395692
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