THE study of dentistry is by no means confined to the mouth and teeth. In fact, initial courses are designed “not to treat teeth but to treat people with teeth.” Such training is essential when we learn, for example, that the adage ‘the eyes are the windows to the soul’ may be accurate, as humans learn in early childhood to manipulate facial expressions to fit a given social situation, which in turn allows them to engage in deceitful behaviour. A person who is angry with their superior may display a social smile rather than an angry scowl when asking for a raise.

When observing others, most people focus on the lower part of the face. However, if a person’s true feelings are “leaked” to the observer, they are more likely to appear on the upper face and may easily be missed. Studies show that the lower portion of the face (nose, lips, and cheeks) is more active than the upper face (eyes, brows, and forehead) when individuals engage in deceitful intentions.

To better understand the brain’s recognition and processing of facial manifestations of emotion, researchers briefly showed 50 people line drawings of human faces displaying different emotions on the upper versus lower face, including happiness, sadness, anger, fear, surprise, and neutrality. Participants viewed the drawings in either the left or right visual field and most often identified the lower face emotion, regardless of the visual field. When subjects were instructed to focus on the upper face, they did so best when pictures were shown in the left visual field (processed by the brain’s right side). However, most continued to identify the lower facial emotion when viewing in the right visual field (processed by the brain’s left side).

Recognition of emotional displays on the lower face appears to be processed by the brain’s left hemisphere as part of the social- or learned-emotional system, whereas emotional displays on the upper face appear to be processed in the brain’s right hemisphere as part of the primary- or inborn-emotional system. These findings help us gain a better understanding of the neurological basis for effective communication, which will enhance a physician’s ability to assess how diseases, such as stroke and dementia, alter these functions.

People may naturally focus on the lower face to aid in speech comprehension during a conversation, especially in noisy environments. Social conventions may also play a role, as many cultures consider it unacceptable to look someone directly in the eyes, fearing the “evil eye.” This may be interpreted as aggressive or threatening behaviour similar to those observed in certain animal species.

A natural curve for acquiring the skills to read facial displays of emotion begins in early childhood. We certainly can train ourselves to pay more attention to upper facial displays to better read a person’s true emotional state. For example, judges can learn to detect if a person may be guilty of a crime by reading their facial expressions when first confronted by an accuser in court. However, this ability has a downside due to social conventions.