The way in which human and primate brains process and interpret facial expressions has been clarified in new studies.
The studies have also touched on the role of facial mimicry in everything from deciphering an unclear smile to establishing relationships of power and status.
Facial mimicry - a social behaviour in which the observer automatically activates the same facial muscles as the person she is imitating - plays a role in learning, understanding, and rapport.
The new findings show that:
Special brains cells dubbed "eye cells" activate in the amygdala of a monkey looking into the eyes of another monkey, even as the monkey mimics the expressions of its counterpart.
Social status and self-perceptions of power affect facial mimicry, such that powerful individuals suppress their smile mimicry towards other high-status people, while powerless individuals mimic everyone's smile.
Brain imaging studies in monkeys have revealed the specific roles of different regions of the brain in understanding facial identity and emotional expression, including one brain region previously identified for its role in vocal processing.
Subconscious facial mimicry plays a strong role in interpreting the meaning of ambiguous smiles.
Another recent finding discussed shows that early difficulties in interactions between parents and infants with cleft lip appear to have a neurological basis, as change in a baby's facial structure can disrupt the way adult brains react to a child.
The findings were presented at Neuroscience 2012, the annual meeting of the Society for Neuroscience and the world's largest source of emerging news about brain science and health.
"Today's findings highlight the role of facial expressions in communication and social behaviour," said press conference moderator Ruben Gur, PhD, of the University of Pennsylvania, an expert on behaviour and brain function.
"Brain circuits that interpret the face appear ever more specialized, from primate 'eye cells,' to brain feedback that enables us to discern meaning through facial mimicry," Gur added.
This research was supported by national funding agencies, such as the National Institutes of Health, as well as private and philanthropic organizations.