Smiling is often considered a universal signal of joy and happiness. But did you know that not all smiles are created equal? Anatomically speaking, there are at least two distinct types of smiles: the Duchenne smile and the non-Duchenne smile.
Named after 19th-century French neurologist Guillaume Duchenne de Boulogne, the Duchenne smile is associated with genuine happiness. This type of smile activates two key muscle groups: the risorius and the zygomaticus major muscle at the corners of the mouth, as well as the orbicularis oculi muscle around the eyes. The combination of these muscle contractions produces the familiar “crow’s feet” and warmth associated with a sincere smile.
On the other hand, non-Duchenne smiles, often seen in fake or polite expressions, usually only involve the muscles around the mouth. The eyes remain wide or indifferent, giving the smile a more mechanical and insincere appearance.
Both types of smiles depend on cranial nerve VII, also known as the facial nerve, which sends signals from the brain to the muscles of facial expression. However, there is a key neurological difference between Duchenne and non-Duchenne smiles. Duchenne smiles are often generated by the limbic system, the brain’s emotional core, while non-Duchenne smiles are more under conscious cortical control, originating in the motor cortex.
Our ability to detect emotional authenticity, particularly in smiles, is deeply ingrained in our evolutionary history. Studies show that even infants as young as ten months old can distinguish between real and fake smiles. This ability may have helped our ancestors assess trustworthiness, recognize allies, and avoid deception.
In modern life, our sensitivity to facial nuance continues to be important. Politicians, customer service workers, and public figures often rely on social smiles to navigate complex interpersonal interactions. While fake smiles serve important social functions like smoothing awkward interactions and signaling politeness, sustaining these smiles without genuine feeling can be emotionally exhausting.
As we navigate the age of AI, where synthetic faces are programmed to replicate human expressions, the challenge remains: how do you fake authenticity? Engineers can program a smile, but without the micro-contractions around the eyes, many expressions still seem disingenuous.
So, next time you’re trying to decode someone’s expression, pay attention to the eyes. The orbicularis oculi muscle rarely lies. A genuine smile, with muscle contractions both around the mouth and eyes, is a true indicator of happiness and sincerity.
