The 19th-century use of localized electrical faradization to photographically map human facial expressions is one of the most fascinating intersections of early neurology, psychology, and photography. This pioneering work is almost entirely attributed to one man: the French neurologist Guillaume-Benjamin-Amand Duchenne (often known as Duchenne de Boulogne).
In 1862, Duchenne published his magnum opus, Mécanisme de la physionomie humaine (The Mechanism of Human Facial Expression). Through this work, he sought to decode the anatomical "grammar" of human emotion.
Here is a detailed explanation of his methods, philosophy, and enduring legacy.
1. The Method: Localized Electrical Faradization
Prior to Duchenne, anatomists studied facial muscles by dissecting cadavers. However, dead tissue could not demonstrate how muscles dynamically interacted to create complex expressions.
Duchenne utilized faradization, a technique named after Michael Faraday, which involved the application of alternating electrical currents to biological tissue. Duchenne invented a non-invasive method called "localized faradization." By placing two metallic electrodes directly onto the surface of the skin on the face, he could deliver a precise electrical shock to a single, specific muscle or muscle group.
This current forced the muscle to contract involuntarily. By doing this, Duchenne could isolate the exact mechanical function of every individual facial muscle, determining which muscle was responsible for a frown, a look of surprise, or a smile.
2. The Role of Photography
Electrical muscle contractions are fleeting; they twitch and release faster than the human eye can thoroughly analyze, and certainly faster than an artist can draw. Furthermore, Duchenne distrusted artistic renderings, believing that painters and sculptors were heavily biased by subjective interpretation and artistic tradition.
To capture the objective anatomical truth of these expressions, Duchenne turned to the nascent technology of photography. Collaborating with a young photographer named Adrien Tournachon (brother of the famous photographer Nadar), Duchenne used the camera to freeze the electrically induced expressions in time. This resulted in a haunting, profound series of images showing Duchenne, dressed in formal 19th-century attire, wielding metal probes against the contorted faces of his subjects.
3. The Subjects
Because electrical shocks to the face are highly painful, Duchenne had to find specific subjects for his experiments. His primary model was an elderly man, often described as a shoemaker, who suffered from severe facial anesthesia (a neurological condition that rendered his face completely numb).
Because the man could not feel the painful shocks, Duchenne was able to experiment on him extensively. Duchenne noted that the man had a naturally dull, expressionless face, making him the perfect "blank canvas" onto which Duchenne could electrically paint any human emotion. Duchenne also photographed other subjects, including a visually impaired woman and an anatomist, to demonstrate how these muscle mechanics applied across different faces.
4. Philosophy: "The Orthography of the Soul"
Duchenne was a deeply religious man. He did not view his work as merely mechanical; he believed he was uncovering divine design. He posited that the Creator had endowed humans with specific facial muscles solely for the purpose of communicating the emotions of the soul.
By mapping which muscles produced which expressions, Duchenne believed he was compiling the "orthography" (the standardized spelling or grammar) of the soul's language. He wanted to provide artists with a scientifically accurate reference manual so they could depict human emotion with absolute anatomical truth.
5. Key Discoveries: The "Duchenne Smile"
Duchenne’s most famous and enduring discovery was the anatomical difference between a genuine, joyous smile and a fake, polite smile.
Through his electrical mapping, he discovered that a fake smile involves only the zygomaticus major muscle, which pulls the corners of the mouth upward. However, a genuine smile of pure joy requires the involuntary contraction of a second muscle: the orbicularis oculi, which crinkles the skin around the eyes. Duchenne noted that this eye muscle cannot be contracted willfully; it only responds to true emotion.
Today, in modern psychology and neurology, a genuine smile is still officially referred to as a "Duchenne smile."
6. Legacy and Impact
Duchenne’s photographic mapping had a profound impact on multiple fields: * Charles Darwin: Duchenne's work directly influenced Darwin. Darwin used many of Duchenne’s photographs in his seminal 1872 book, The Expression of the Emotions in Man and Animals, arguing that facial expressions are biologically innate and evolutionarily inherited, rather than culturally learned. * Neurology: Duchenne's technique of localized electrical stimulation laid the groundwork for modern electromyography (EMG) and the diagnosis of muscular and neurological disorders (such as Duchenne muscular dystrophy, which is named after him). * Art and Physiognomy: His photographs remain a vital reference point in the history of medical photography, demonstrating how the camera was used as a tool for empirical scientific evidence.
In summary, Duchenne de Boulogne’s use of localized faradization and photography in the 19th century was a revolutionary attempt to merge physics, anatomy, and visual art. By shocking the facial muscles of his numb patients, he successfully mapped the biomechanics of human emotion, leaving a legacy that still dictates how we understand the human face today.