Can expressions be asymmetrical?
The ability to efficiently express our own emotions is as vital to survival as to interpret others’. And it is not surprising that in a study titled Evolution of facial expression published in Science in 1963, it was stated that “emotional expressions indicate the likely future behavior of the displaying human and thus communicate intentions and desires”. Something that we can all relate to after more than one year of wearing compulsory face masks.
In an interesting review published in 2018 in the journal Progress of Brain Research, Dr. Annukka Lindell outlines that when humans express emotions through facial expressions, we do it asymmetrically. This may appear initially surprising, as we are rarely conscious of differences in expressivity between the two sides of the face.
Research suggests that people who are naturally more emotionally expressive are more inclined to pose for photos with their left cheek forward. Similarly, when asked to pose explicitly expressing as much emotion as possible, people are more likely to offer their left cheek. Moreover, when recorded, some eye movements confirm that both infants and adults intuitively spend more time looking at the more expressive left hemiface.
But let’s have a closer look on how it works on a neuromuscular level. The muscles of the face are predominantly innervated by the facial nerve. Whereas the upper face (e.g. the frown, eyebrows) is under control of both halves of the brain (bilateralcortical), the lower two-thirds of the face is contralaterally innervated. In other words, from the lower eyelid downward, the left side of the face is controlled by the right hemisphere of the brain, and the right side of the face is controlled by the left hemisphere. And, because the right brain hemisphere has an emotional dominance, as a consequence of this contralateral innervation of the lower face results in greater expressivity on the left rather than the right hemiface, where evidence shows that emotions are more intensely expressed.
Mind-blowing, isn’t it? If you want to double check the study, try it out yourself! Grab your phone and start posing in front of the camera. Can you notice whether you are grinning or grimacing, if your facial expression shows stronger emotions on the left side of the face?
Cortical projections of cranial nerve VII: the facial nerve. The upper faceis bilaterally innervated, whereas the lower face is innervated contralaterally: the right hemisphere controls the left hemiface, and the left hemisphere controls the right hemiface (Lindell, 2018). Image courtesy of Patrick J. Lynch, medical illustrator. Creative Commons Attribution 2.5 License 2006