How Our Brains Uses Oxytocin to Distinguish From Real and Posed Smiles

By Alya Khoury

Recently, I bought a box of cookies. This made two people smile. First, the lady at the cash register as she politely wished me a nice day; then, my roommate, who couldn’t help herself from beaming as I unloaded her favorite snack from the bags of groceries. One box of cookies, but two very different smiles. But what was truly different about them? How could I tell? 

A group of researchers at Emory University asked a similar question. They conducted a study to explore the biological mechanisms behind how people judge a smile as genuine or posed. The researchers found potential genetic and neural evidence for the distinction between smiles. They saw that both types of smiles activate the same brain regions associated with facial recognition and emotional processing, however due to genetic differences some people are more sensitive to the subtle differences. 

Smiles are a universal expression of joy, but not all send the same message. When we experience genuine happiness, our facial muscles contract almost involuntarily. As James Rilling, a professor of psychology, researcher of Darwinian Neuroscience at Emory University, and the senior author of the study, explained “When you see something and it brings you joy, it’s almost a reflexive facial expression.” This reflex smile is controlled by the basal ganglia, a region deep in the brain. “It’s kind of more of an instinct” he added. 

But there’s another kind of smile—the conscious, polite one. This is often used to appear friendly but doesn’t necessarily reflect feeling happy. Rilling calls it the “flight attendant smile”—a smile that can be produced on demand. This type of expression is controlled by the cortical areas of the brain, which involve more conscious processing. 

“A lot of human behavior is trying to fool other people, sometimes not necessarily broadcast sincerity” said Dr. Robert Froemke, a professor of neuroscience and  otolaryngology at New York University Grossman School of Medicine, and researcher of oxytocin. “A lot of social signaling, especially overt expressions, are designed to convey a particular message on purpose, which can oftentimes be masking the true intent.

What these Emory researchers wanted to know was how our biology allows us to navigate between true smiles, and posed. 

In the study, researchers measured brain activity when participants viewed genuine and posed smiles. They found that both types of smiles activated areas of the brain responsible for face recognition, empathy, and emotional processing. However, only genuine smiles triggered the medial orbitofrontal cortex, a region associated with rewarding experiences. This suggests that authentic smiles are perceived as more emotionally gratifying.  

To see how satisfying experiencing smiles can be, the researchers offered the participants money versus each smile. Participants were more likely to choose viewing a genuine smile over receiving money, but when offered a posed smile, they were more likely to choose the money. This shows how powerful genuine emotional expressions can be, even at a subconscious level. A genuine smile can activate the brain’s reward centers, making us feel connected and valued. In contrast, a posed smile, while still polite, lacks the emotional reward component. 

Beyond the brain’s immediate response to smiles, researchers also looked at the genetic component behind how we judge smile authenticity, focusing on the oxytocin receptor gene. 

Oxytocin is a central molecule to understanding social behavior. As Rilling said, “there’s probably no other molecule that’s as important [as oxytocin] when we’re thinking about the biology of social behavior.”  Rilling explained that oxytocin “enhances social reward,” meaning it amplifies the positive feelings we get from social interactions. This could explain why authentic smiles have this emotional gratification effect—our brains, primed by oxytocin, become more attentive and engaged with meaningful social stimulus.   

For molecules like oxytocin to perform, they need to bind to receptors. For these receptors to exist, they need to be encoded by genes in our DNA. 

The oxytocin receptor gene is polymorphic, meaning different people have different versions of the gene. The researchers discovered people with a specific version of the oxytocin receptor gene —those with a homozygous arrangement—were less able to distinguish between genuine and posed smiles. This suggests that the ability to read social cues like smiles could possibly be influenced by genetic arrangements. Rilling, however, cautioned against jumping to quickly to such conclusions. Instead he suggested that these findings open the door for more research on the relationship between oxytocin and the social brain. 

Studying oxytocin has become increasingly interesting to many neuroscientists. Dr. Froemke, compared brain research to building a puzzle, “if you’re going to solve an actual puzzle, most of us start with, the edge pieces or corners, and then work to fill in.” Oxytocin, he added, serves as a key edge piece.   

The findings of this research not only uncover key biological mechanism but also offers insight into the complex nature of human interaction. Rilling and his team of researchers are now investigating oxytocin and caretakers of people with dementia. Froemke has studied the relationship of mothers, oxytocin, and the bond to their children. Other researchers have looked at oxytocin’s role in facial mimicry, laughter authenticity, emotional literacy, attraction, and more of these key behaviors that make us human.  

As Rilling explained, “There’s nothing anywhere near as obvious in other non-human species as our smile.” Humans rely heavily on social cues, and our ability to read those cues—whether they’re genuine or not—plays a crucial role in our social dynamics. A genuine smile can create trust and connection, while a posed smile might serve a strategic purpose, such as maintaining politeness in social settings. 

The findings from this study show just how intertwined our biology is with our social behavior. Smiles are just one window into how we have uniquely evolved to optimize human connection. But the research also highlights the incredible diversity within our species – no two brains or genetic makeups are exactly the same. This complexity leaves us with more questions than answers, fueling the ongoing research to understand what it means to be human.  

As Dr. Froemke said, “I think that another reason why we’re all so interested in this one molecule is because, really what we’re interested in is each other.”