Do monkeys make faces intentionally?
A new study suggests that primate facial expressions may not be just reversible.
Macaques’ threatening smiles and friendly lip-smacking may be partly intentional.
Christoph Lehneff/Getty Images
Facial expressions are central to social life, yet scientists still do not fully understand how the brain produces them. For decades, a dominant theory has held that what you see on your face is largely a emotional reflection– An honest, automated readout of what you feel inside. But that view struggles to explain the fact that we often adapt our faces to the moment: We’ve all smiled politely during a dull date, or tried to. No Smiling while holding a royal flush.
To find out what’s going on in the brain during facial expressions, researchers turned to rhesus macaques, Old World monkeys whose facial muscles and neuroanatomy are similar to those of humans. They recorded neural activity While in the laboratory the animals interacted with each other as well as with digital avatars and videos of other macaques. Team results, published today Science, What came as a surprise: The monkeys’ expressions, ranging from a threatening face to a friendly “lip-chasing” face, were generated by both the medial cortex and the lateral cortex.
These brain areas were long thought to be work independentlyThe medial side controls behavior and lateral voluntary actions including spontaneous emotional expressions. “Our study didn’t show that at all,” says Gina Ianni, co-lead author and neurology resident at the University of Pennsylvania. “This showed that all areas participated in the production of all types of facial expressions.”
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However, the two sectors moved at different speeds. “There’s a different speed of the way they encode information,” says co-lead author Yuriria Vazquez, a neuroscientist at Rockefeller University. Activity in the lateral cortex shifted rapidly, over milliseconds, to coordinate the rapid facial movements that make up spontaneous social interactions. In contrast, things happen more leisurely in the medial cortex, perhaps allowing it to track slower-changing contextual factors – such as “Has the alpha male stopped threatening me?”,Which affect facial expressions. Furthermore, both neural patterns appear before facial movements, suggesting that the brain prepares expressions in advance.
All this raises a question: Do macaques deliberately plan the faces they make? This is what evolutionary psychologists Bridget Waller and Jamie Whitehouse of Nottingham Trent University in England have explained. a comment On new study. If facial expressions are partly voluntary, they may be less like emotional mirrors and more like “tools for social influence”, as Waller and Whitehouse put it. At least, they appear to arise from the complex interplay between emotion and cognition.
Alan Fridlund, a social and evolutionary psychologist at the University of California, Santa Barbara, who was not involved in the study, has no problem believing that macaques use their faces strategically. But he doubts that staged, laboratory-bound interactions can capture the full reality of primate communication, or the neural activity underlying it; Ideally, future research will take place in monkeys’ natural environments. Still, Fridlund says, the new study “tells us in infinitely more detail how we can investigate the neuroscience of facial displays.”
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