Say Cheese! Why Posed Smiles Look Fake

By Phoebe Matthew

We have all experienced our smiles never looking natural in pictures - too broad, lopsided, or just plain awkward. Surprisingly, this common and seemingly simple phenomenon gives us insight into the functions of various areas of the brain. The brain is often seen as a group of discrete parts that control various aspects of life, including emotions, movement, decision making, and memory. This discrete nature usually goes unnoticed in everyday life, where the different parts of the brain are always acting together. However, comparing our spontaneous smile to our “posed” smile, as we may call it, gives us some insight into two separate systems in our brains. Spontaneous smiles are defined as a smile coming from an emotional response, and posed smiles can be defined as voluntary smiles that are not triggered by an emotion. Although this distinction may be too rigid to be applied to everyday life, it is beneficial when discussing the different parts of the brain as they relate to each other (Korb et al., 2008).

Before getting into what we can’t see, let’s consider the differences we can see. Studies have shown that the spontaneous smile, also called the Duchenne smile, involves the zygomatic major muscle, responsible for lifting your cheeks. It also activates the orbicularis oculi muscle, which is responsible for movement around your eyes. Posed smiles also involve the zygomatic major muscle, but the activation of the orbicularis oculi is largely absent, meaning there is less squinting of the eyes compared to genuine smiles (Ekman et al., 1990). Many of you may have already noticed this phenomenon when it comes to your own smile, especially when taking pictures. Now that we know the visible differences, we can ask the question, “why?” This question takes us to the brain.

Movements are controlled by the primary motor cortex, which is known as M1. Research has shown that this area of the brain is more active during posed smiles, but is not necessary for your spontaneous smile. With spontaneous smiles, the nervous system acts in a very complex way, with involvement of the basal ganglia, thalamus, supplementary motor cortex, amygdala, and hypothalamus. All of these are intricate structures spread throughout the brain that receive sensory input and produce motor output. Many of these structures, such as the amygdala, hypothalamus, and thalamus, are controlled by the limbic system, the primary system that identifies emotions and integrates them into actions (Root & Stephens, 2003). Thus, the limbic system,(at least in part) controls our spontaneous smile as it is an emotional reaction, whereas the primary motor cortex seems to be more involved in posed smiles. Connecting this to our physical observations of the differences between the posed and spontaneous smile allows us to conclude that the orbicularis oculi muscles are much harder to activate voluntarily than the zygomatic major muscles, creating the subtle but significant difference between the two smiles.

Our analysis of the differing brain region activation has allowed us to identify two different systems in the brain relating to our spontaneous emotional response and voluntary facial expressions. The processes behind our two different smiles have also been proven to differ in relation to the brain hemispheres involved. These studies have typically been done on split-brain patients, who are individuals with a severed or missing corpus callosum (the nerve fibers connecting the left and right hemispheres) and thus have no communication between the two lobes of the brain. In these individuals, when the instruction to smile was shown to their left visual field, controlled by the right hemisphere of the brain, none of the patients smiled in response. On the other hand, when the instruction to smile was shown to their right visual field, controlled by the left hemisphere of the brain, the right side of the patient's face began a posed smile before the left side of the face was activated. This indicates that the left hemisphere is primarily responsible for our voluntary facial expressions, including our posed smile. The patient's left side eventually was activated due to slower, indirect neural communication between the hemispheres. Regarding a spontaneous smile, the patients were able to respond bilaterally with no delay (Gazzaniga & Smylie, 1990). This allows us to conclude that the spontaneous smile involves both hemispheres and is overall a more complex process, compared to our posed smiles, which primarily is controlled by the left hemisphere. 

So the next time you try to replicate your smile in a picture, you can focus on trying to activate your orbicularis oculi muscles, or you can just take it as a reminder of the complexity of your brain, with each function being controlled by different structures and systems.

References

Ekman, P., Davidson, R. J., & Friesen, W. V. (1990). The Duchenne smile: Emotional expression and brain physiology: II. Journal of personality and social psychology, 58(2), 342.

Gazzaniga, M. S., & Smylie, C. S. (1990). Hemispheric mechanisms controlling voluntary and spontaneous facial expressions. Journal of Cognitive Neuroscience, 2(3), 239-245.

Korb, S., Grandjean, D., & Scherer, K. (2008, September). Investigating the production of emotional facial expressions: a combined electroencephalographic (EEG) and electromyographic (EMG) approach. In 2008 8th IEEE International Conference on Automatic Face & Gesture Recognition (pp. 1-6). IEEE.

Root, A. A., & Stephens, J. A. (2003). Organization of the central control of muscles of facial expression in man. The Journal of physiology, 549(1), 289-298.