Duchenne’s smile. The neurologist found the key to the most authentic smile

We consider the French physician Duchenne de Boulogne, born in 1806, to be one of the fathers of neurology. His contemporaries added “de Boulogne” (from the name of the town he came from) to his surname, so that he would not be mistaken with Dr. Duchesne, a popular doctor of the Parisian society. Based on Galvani’s discoveries, Duchenne developed a science he called electrophysiology. In contrast, neurology owes him the first descriptions of several nervous and muscular disorders, an understanding of the conductivity of nerve pathways, and diagnostic innovations, including deep tissue biopsies, nerve conduction tests (NCS), and clinical photography.

1. The Duchenne smile is considered to be the most authentic smile
2. With this smile, two muscles contract naturally: the zygomatic muscle and the circular muscle of the eye
3. Guillaume Duchenne, a XNUMXth-century neuroscientist, studied how facial muscles are responsible for facial expressions
4. You can find more such stories on the TvoiLokony home page

A doctor instead of a fisherman

Guillaume Duchenne was born in Boulogne-sur-Mer to a family where men had worked at sea for generations. However, he was so fascinated by science that, at the age of 19, he passed his high school diploma against the will of his father, and then he was educated under the supervision of many eminent doctors. In 1831, he graduated from medicine in Paris and … returned to his homeland, where he started an apprenticeship. In the same year he got married. Two years later he was already a widower because his wife died of maternal fever. The mother-in-law blamed him for the death of her daughter and took his only son with whom he met only at the end of his life.

In the 30s, a young doctor began to experiment with “therapeutic electropuncture”, a method involving stimulating the muscles with an electrical impulse administered under the skin. In the following decade, after a short and unhappy second marriage, he returned to Paris to continue his research.

He worked on the use of electricity as a tool for physiological experiments, and the use of alternating current allowed him to precisely stimulate a selected muscle bundle. Thanks to this method, he described several diseases and located their origin. To date, many myopathies are named after him: Duchenne muscular dystrophy, Duchenne-Aran spinal muscular atrophy, Duchenne-Erb paralysis, Duchenne disease, and Duchenne paralysis (progressive bulbar palsy). He also developed the biopsy technique by developing a tool for collecting tissue samples inside the body.

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He defined human facial expressions and associated a certain facial expression with a specific muscle or group of muscles. Duchenne identified thirteen basic emotions whose expression is controlled by one or two muscles. To stimulate them, he applied a faradic shock (he pressed electrified metal probes against the surface of various facial muscles).

The artistic aspect of his work is also extremely interesting. As a photographer, he meticulously registered facial expressions and was the first to illustrate neurological texts with photographs. His monograph “The Mechanism of Human Physiognomy”, widely discussed by contemporaries, as the first study on the physiology of emotions, was reflected in Darwin’s later works.

Despite his unconventional approach to science and difficult relationships with other doctors, his determination secured him international success and the position of an outstanding neurologist and scientist, although during his lifetime he did not receive the honor of being elected to the French Academy of Sciences. Duchenne died of a stroke in 1875 at the age of 68.

“I want to change both the history of medicine and photography”

Duchenne wanted to find out how the facial muscles generated the facial expressions he believed were directly related to the soul resulting from “moving the spirit”. He triggered muscle contractions using electrodes, registering the resulting, often grotesque, facial expressions with a camera invented 15 years earlier. He published his discoveries with unusual photographs of human faces in 1862 in the book “Mechanism of Human Physiognomy”.

Like physiognomists and phrenologists before, Duchenne believed that the human face was a map and that its features could be codified. However, unlike other scholars of the era, who described the character of a man by the shape of his head, he was skeptical of the ability to express moral attitudes through facial expressions. Rather, he was convinced that reading facial expressions revealed “the emotions of the soul.” He also believed that “perfect features” can be captured in a similar or even better way than in Greek art.

Believing that he is studying the language of facial expressions given by God, Duchenne writes: “Our Creator was able in his wisdom or – forgive this way of speaking – in the realization of a divine fantasy … to set in motion individual muscles, one or more at a time, when he wished for characteristic signs of emotions. Once the language of facial expressions was created, it was enough for people to instinctively express their feelings by flexing their muscles and the language became universal ”. Thus, in order to convey similar emotions, all human races were endowed with the same facial expressions.

He was convinced that the “truth” could only be effectively conveyed by means of photography, as facial expressions were too fleeting to be drawn or painted. “Only photography”, he writes, “real as a mirror, could achieve the desired perfection”.

He collaborated with the talented photographer Adrian Tournachon (the younger brother of Felix Nadar), specializing in portraits, and over time he mastered the art of taking pictures himself. Mechanism was the first publication devoted to expressing human emotions illustrated with photographs. He used live models, five of which were his patients. The main model was “an old, toothless man with a thin face, whose features, while not being absolutely ugly, were approaching the usual triviality”.

Through his experiments, Duchenne tried to capture “the conditions that aesthetically make up beauty”, while he described facial expressions as “gymnastics of the soul”. Therefore, he referred to his criticism of his use of an old man with the words: “any face can become spiritually beautiful by accurately conveying its emotions”, adding that since the patient suffered from facial paralysis, he could experiment with the muscles without causing pain.

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To locate and identify facial muscles, Duchenne relied on the work of Charles Bell, although he did not share the Scottish anatomist’s interest in the facial expressions of mentally ill people. He did not photograph them, most likely for aesthetic reasons – he just did not consider the expression of madness to be socially acceptable.

For Duchenne, photos are an argument for a connection between his research and the work of eminent artists. He used strong lighting analogous to Rembrandt’s style, whose aesthetic authority was to confirm the truth of the photos. He also referred to other famous Baroque painters, including Caravaggio. He argued that by varying the lighting effects, it was possible to obtain more “truth and clarity” of individual types of expression.

An exact imitation of nature was for him a sine qua non condition for the creation of an outstanding work of art in every era, and although he praised the ancient Greek sculptors for undoubtedly achieving the ideal of beauty, he pointed out anatomical errors and neglect of emotions. He even questioned the talent of the Greek sculptor Praxiteles, author of the figure of Niobe: “Would Niobe be any less beautiful if the terrible emotion of her spirit raised the arch of her eyebrow, as nature does, and if a few lines of sadness crinkled the middle of her forehead?” On the contrary, nothing is more moving and alluring than the expression of pain on a young, usually serene, forehead ».

Admired but also criticized

Responses to Duchenne’s facial expressions were mixed. One of the most respected scientific journals of the time, the Journal des Débats, praised him for his contributions to animating interest in facial expressions. The reviewer claimed that The Mechanism, due to the usefulness of illustrations, is an important publication for both physiologists and artists.

The most famous critic of the work in scientific circles was Duchenne’s friend Charles Darwin, who, moreover, used some of the Frenchman’s photos to illustrate his 1872 book “The Expression of Feelings in Man and Animals”. Even so, he opposed many claims. First, he argued that Duchenne was unable to explain why muscles responded to specific emotional states in certain ways. He based his objection on the idea that they operate in groups, not individually. For Darwin, Duchenne’s findings were inaccurate, as the electrical impulse only triggered individual muscle responses. Second, he did not like to limit the experiments to just humans. He argued that the muscle movements of all organisms can be traced back to a similar evolutionary origin. Meanwhile, Duchenne insisted that facial expressions must be associated with the “Creator” and not with the process of evolution.

Darwin also conducted a counter experiment to refute Duchenne’s main thesis that every facial expression is linked to specific emotions. He showed some of Duchenne’s photos to “educated people”, concealing the captions. Viewers had difficulty recognizing emotional states, which proved that the French’s conclusions were largely subjective and based on text-image juxtapositions.

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However, the most devastating criticism came from Pierre Gratiolet, another scientist who studies facial expressions. He questioned the very meaning of Duchenne’s experiments. He argued that they were irrelevant as facial expression was artificially induced. Thus, the examination violated the most important principle of physiognomy: facial expression is the result of internal, not external, stimuli. So all of his findings are invalid because they say nothing about the expression of real emotions, but rather a simulation created by electricity.

What is the Duchenne smile?

A smile is a powerful weapon. Darwin paid attention to him, and modern scientists have found that it is the smile described by Duchenne that particularly influences emotions. You can see it around the eyes, in the wrinkled outer corners, it is a smile that we recognize as an authentic expression of happiness. It appears due to the interaction of two muscles. The zygomatic major muscle lifts the corners of the mouth, while the orbicularis oculi (eye circular muscles) – the cheeks, causing the so-called crow’s feet.

Why is the Duchenne smile so important to us? Because it improves your mood. It has been shown that smiling changes our mood, as information from facial muscles can affect our emotional state. By engaging the muscles that we use to smile, we stimulate the parts of the brain that control emotional responses.

In 2019, researchers identified the impact of the Duchenne smile on young people who felt excluded, and concluded that it helps to “spontaneously regulate emotional experiences”, for example when confronted with peers. Neurobiologist Peggy Mason, who described the effects of Duchenne’s smile, said it could be contagious. It is one of those facial expressions that creates a “social bond” that allows us to feel empathy. When we look at the other person and smile, it creates closeness, a relationship of healing power.

Smiling also changes our body’s reaction to stress. In 2012, researchers gave study participants two sets of stressful tasks, instructing selected groups to smile at each other during the most difficult phase of the experiment. It turned out that in the smiling group, the heart rate during recovery from stress was at the lowest level, and those who tried to imitate Duchenne’s smile were the most calm. So, in a nervous situation, it brought both physiological and psychological benefits.

Research also shows that a smile is convincing, it is associated with positive experiences, it influences how others see us. It makes us trustworthy, and the environment reacts positively to us.

Apparently 80 percent. people are unable to train the “Duchenne smile” because we have no control over the muscles around the eyes that signal it. However, a 2009 study by Krumhuber and Manstead challenges this thesis. As much as 83 percent. test participants were able to fake the famous smile. The researchers also checked how we perceive true and false Duchenne smiles by playing videos and showing photos. It turned out that the false ones were easier to spot during the projection, but the allegedly key wrinkles around the eyes did not help much.

The distinction between a true Duchenne smile and a false one was based on dynamic processes such as the duration of the smile, symmetry of facial expressions, and whether other areas of the face communicated conflicting emotions.

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