Mirror Mirror on The Wall: The Science of Mirror Neurons

You've probably heard that yawning is contagious. But this simple action is actually an entryway to a developing field in neuroscience that might bring more information about shared social behaviors.

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Have you ever noticed how, when one person yawns in a group, another person is soon to follow?  

It’s a common idea that yawning is contagious, spreading from one person to others nearby. It might be hard to distinguish a seemingly far-fetched claim from myth or fact, but, shockingly, this idea is supported by scientific evidence. The act of yawning is actually a form of mirroring, mediated by distinct “mirror neurons” in the brain that govern imitative behaviors in humans and even some animals, evidence of a socially conscious instinct. 

First, let's understand what a yawn is and the biological need behind it. There is no completely agreed-upon reason; however, there are a few plausible explanations. One hypothesis is that yawning counteracts a buildup of carbon dioxide in the body, often due to a recent lack of deep breaths known to accompany fatigue or other chemical changes. According to speech scientist Douglas Parham in a PBS News article, a yawn could serve as “a special respiration,” as it “builds up oxygen quickly, while expelling carbon dioxide more than a deep breath.” 

Another reigning theory is that yawning regulates brain temperature, for when the brain is running warm. Andrew Gallup from Princeton University reported on the “brain cooling, or thermoregulatory, hypothesis,” extrapolating from a study he helped conduct, in which rat brain temperatures were measured before and after yawning. 

“The cooling effect of yawning is from enhanced blood flow to the brain caused by stretching of the jaw, as well as countercurrent heat exchange with the ambient air [from the breath]," Gallup said in the study.

Clearly, yawning seems to correlate with an assist in either oxygenation or thermal normalization of the brain. 

However, this doesn’t explain why an individual’s effort to support these processes through yawning would be replicated in an observer. That effect, according to neuroscientist James Giordano, is due to a phenomenon called social mirroring involving mirror neurons in the brain. 

Mirror neurons were first discovered at the University of Parma by Giacomo Rizzolatti and his team in the 1980s. They observed that neurons in the premotor cortex, F5, in macaque monkeys would fire during simple actions, such as reaching for objects. Using electrodes to isolate F5 neuron activity, they tested responses to different objects and when these monkeys passed them to each other. They realized that a monkey picking up an object experienced specific neuron firing in the F5 region that was actually replicated in the monkey receiving the object from them. A deeper dive showed that the same neurons would fire in a monkey that grabbed a peanut, and in a monkey watching the experimenter grab said peanut. This discovery provided an entirely new avenue of social behaviors to investigate. 

“We were lucky, because there was no way to know such neurons existed,” Rizzolatti said in the study.” But we were in the right area to find them.” 

As researchers have explored these “mirror neurons” in humans, they have been met with some struggles in identifying the exact region and depth to which these neurons work in humans. However, it's generally agreed upon that to some extent, “human mirror neurons, operating in our highly sophisticated brains, are responsible for a wide array of human social behaviors, from imitating someone else’s actions to learning music to feeling empathy.” 

Going back to the original question of why yawning is contagious, it is concludable that, as a behavior that is beneficial and an extension of connection, the act of yawning is reciprocated for the reason of collective well-being. 

Zhou Feng-Chen of Washington University’s Center for the Study of Itch has reasoned through his conducted study of social scratching in mice that, “when animals mimic others, they must be recognizing a useful behavior,” instinctively deciding to follow as well. In the case of wild animals, it makes sense to corroborate helpful behaviors throughout the group in order to avoid disease or harm. 

Neurologist Thomas Scammel from Harvard Medical School chalks it up to something simpler, a vessel of social communication. He recognizes that these behaviors could also function to strengthen social bonds. 

“If someone flashes you a nice, friendly smile,” he said, “you’re likely to smile back.” 

These articles are not intended to serve as medical advice. If you have specific medical concerns, please reach out to your provider.