Have you ever noticed that there are basically two types of smiles: a genuine smile and a fake one? This distinction has been of interest to researchers for quite some time. In fact, the genuine smile has a name. It is called the "Duchenne smile" for the French physician Guillaume Duchenne, who studied the physiology of facial expressions.
The Duchenne smile involves a voluntary and involuntary contraction of two muscles: the zygomaticus major (raising the corners of the mouth) and the orbicularis oculi (raising the cheeks and producing crow's feet around the eyes). A false smile implies the contraction of only the zygomaticus major since we cannot voluntarily contract the orbicularis oculi muscle.
Two different types of smiles
Scientists have discovered that these two types of smiles are actually controlled by two completely different parts of our brain. When a patient with motor cortex damage in the left hemisphere of the brain tries to smile, the smile is asymmetrical and the right side of the smile does not move as it should. However, when that same patient laughs spontaneously, the smile is normal without asymmetry. This means that the genuine smile is controlled by some other part of the brain.
Now when a patient with damage to the anterior cingulate (part of the limbic system) in the left hemisphere tries to smile, there is no asymmetry. The smile is normal. However, when that same patient tries to smile spontaneously, asymmetry appears.
Therefore, the false smile is controlled by the motor cortex, while the movements related to emotions, such as the Duchenne smile, They are controlled by the limbic system (the emotional center of the brain).
A sincere smile that generates positive emotions
In this sense, a Duchenne smile is a natural smile of enjoyment, made by contracting the zygomaticus major muscle and orbicularis oculi muscle. When you see someone show a Duchenne smile, you naturally feel positive emotions for the person smiling. The smile is distinctive, with the mouth turned up (the zygomaticus major), the cheeks raised, and the eye sockets crinkling to create crow's feet (the orbicularis oculi).
Duchenne's is special. The Duchenne smile is different from a non-Duchenne smile for different reasons. First, the Duchenne smile uses both the zygomaticus major and the orbicularis oculi. The non-Duchenne smile does not reach the eyes, but resides only on the lips and possibly the cheeks.
Second, the Duchenne smile is considered a natural smile of enjoyment. In the past, the consensus among researchers was that a true Duchenne smile couldn't be fake. More recent research casts that into question. Now, researchers are spending more time trying to figure out how we benefit and how we can produce the Duchenne smile.
The smile of enjoyment
Why would smiles of enjoyment differ from other smiles? The differences between enjoyment and other smiles originate in functional neuroanatomy. There appear to be two distinct neural pathways that mediate facial expressions; one avenue is for voluntary facial actions, and a second for involuntary and emotional facial actions.
Voluntary facial movements originate in the cortical motor strip of the brain and reach the face through the pyramidal motor system. Involuntary facial movements, such as those involved in an emotional expression, arise mainly from the subcortical nuclei and they reach the face through the extrapyramidal motor system.
How to say that a smile of enjoyment is genuine
As we have indicated above but it is worth noting, in a smile of true enjoyment, the skin above and below the eye is stretched towards the eyeball, and this produces the following changes in appearance. The cheeks are raised; the skin under the eye can accumulate or bulge; the lower eyelid moves up. Crow's feet wrinkles can appear in the outer corner of the eye socket; the skin over the eye is slightly pulled down and inward; and the eyebrows move down very slightly.
A non-enjoyable smile, in contrast, exhibits the same movement of the corners of the lips as the enjoyment smile, but does not involve changes due to the muscles around the eyes. It is in the look above all, in the brightness of the eyes, where you can really appreciate if a person is smiling genuinely, or not.
Fake smiles
We have all laughed falsely at some point in our lives. In a smile, the absence of movement in the outer part of the muscle that orbits the eye (orbicularis oculi pars lateralis, in Latin) distinguishes a false smile from a genuine one. If the smile is mild or moderate in scope, the absence of this movement is easy to detect because no crow's feet are present and the cheeks are not lifted by muscle action, reducing the opening of the eye.
On the other hand, a deliberately made wide smile will produce all of these signs, making the fabrication more difficult to detect, so a much more subtle clue should be sought: a very slight decrease in the eyebrows and the skin between the browbones. and the upper eyelid, which is called the crease of the covering of the eye. This difference is difficult to recognize, and most of the time we are easily fooled by a wide fake smile, which could also explain why people use it as a common emotional mask.
Social smiles
Social smiles, are they genuine or fake? Normally they are false because we do it, "because it should be like that" and not because that smile is actually felt at that moment, at least, in most occasions.
Cultural anthropologists also observed that humans from different cultures smile in situations involving negative and positive emotions, further reinforcing the conclusions of experimental psychologists ... These anthropologists concluded that the meaning of the smile was culturally determined, which in general terms , there were no universal expressions of emotion, and in particular, there were no universal facial expressions of enjoyment, although there are widely used facial expressions of emotions.