A neurologist explains how to spot a fake smile

What is it about fake smiles that make them feel so ungenuine? Why is it so difficult to fake a smile? In 1862, the French neurologist Guillaume Duchenne published his finding that real and fake smiles are actually accomplished using different muscles.

All smiles require that we flex muscles around the mouth, but the difference is the way we involve the muscles around our eyes, called the orbicularis oculi. In a genuine smile, we contract those muscles, pulling in the skin next to our eyes, as you can see in the picture of this handsome fellow:

Wellcome Images

Teeth or no teeth, doesn’t he look genuinely happy to see you (and not at all creepy)? Look at the contraction of the muscles around his eyes. That only happens with smiles that reflect true, happy emotions.

On the other hand, a fake smile doesn’t use those muscles. When forcing a smile, we use a muscle in each cheek, called the risorius, to pull our lips into the right shape, but the eye muscles don’t contract. To demonstrate this, Duchenne electrically stimulated the risorius muscles of his tooth-less friend. Here’s what that smile looked like:

Wellcome Images

There are creases on his cheeks but not around his eyes. The orbicularis oculi muscles are not contracted. The skin around the eyes is not pulled in tightly as it is in the first picture. That is the mark of a fake smile.

The differences in muscle contraction in genuine versus fake smiles illustrate the separation between the habit and the non-habit systems in the brain. When a smile comes naturally to us, one set of muscles is activated. When we use our conscious powers to feign a smile, we alter the pattern of muscle activation, and people around us can tell.

One more example. Recently, I noticed a colleague in the hall of the hospital where I work who was visibly distracted by his smart phone as he walked.

As he passed by me, I asked, “Hey, how’s the patient doing?” He replied, “I’m good. How are you?” The automated response was evidently a response to “Hey, how are you?” which is not what I asked.

With his mind preoccupied by his phone, the doctor replied out of habit. When I asked him about the incident later, he had no recollection of the unfitting remark. I then did a little experiment by asking distracted people similar questions and found that this kind of thing happened a lot (and I know I’ve done it too).

Interestingly, most people I asked about it, like my colleague, also did not remember giving me an inappropriate response.

Our dual control systems involve different regions of our brains and have distinctive effects on behavior, whether in sports or in the way we interact socially. But the incident with my colleague implies that they differ in yet another way: they are associated with separate forms of memory.

Excerpted from NEUROLOGIC by Eliezer Sternberg. Copyright (c) 2016 by Eliezer J. Sternberg. Excerpted by permission of Pantheon, a division of Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

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