Why Yawning Is Contagious - The Neuroscience of Contagious Yawning and Its Deep Connection to Empathy

Contagious Yawning Is Not Unique to Humans

When someone yawns on a train, within seconds the people around them start yawning one after another. This phenomenon is so commonplace that we rarely think deeply about it, yet it is a topic actively studied at the forefront of neuroscience.

Contagious yawning is not exclusive to humans. It has been observed in chimpanzees, bonobos, gelada baboons, wolves, and dogs. Particularly noteworthy is the research finding that dogs respond more strongly to their owner's yawns than to those of strangers. This discovery, published in 2013 by a research team at the University of Tokyo, suggested that contagious yawning is not merely a reflex but is related to social bonds.

Why Do We Yawn in the First Place?

Before discussing contagion, let's clarify the function of yawning itself. Remarkably, the biological purpose of yawning has not been fully elucidated even in the 21st century.

The once-dominant "oxygen deficiency hypothesis" (that we yawn to send oxygen to the brain) has been experimentally disproven. Studies showed that changing oxygen levels did not alter yawning frequency.

The most widely supported theory today is the "brain cooling hypothesis." According to research by Professor Andrew Gallup at the State University of New York, yawning functions as a cooling mechanism for the brain. When we yawn, we inhale a large volume of outside air, which cools the blood vessels in the oral and nasal cavities, and this cooled blood is then sent to the brain. Evidence supporting this hypothesis includes the finding that yawning frequency increases in warmer seasons and that placing a cold towel on the forehead suppresses yawning.

Three Hypotheses for Contagious Yawning

1. The Mirror Neuron Hypothesis

Mirror neurons, discovered at the University of Parma in Italy in the 1990s, are nerve cells that "fire in the same way when observing another person's action as when performing that action oneself." When you see someone pick up a cup, the motor program for picking up a cup is activated in your own brain. This "mirror-like" response forms the basis for understanding and imitating others' actions.

Contagious yawning may also be explained by this mirror neuron system. When you see (or hear) someone else yawn, the motor program for yawning is automatically activated in your brain, and this is output as an actual yawn. fMRI studies have confirmed that the inferior frontal gyrus (a region where mirror neurons are concentrated) is activated during contagious yawning. (You can learn more from books on mirror neurons.)

2. The Empathy Hypothesis

The most intriguing aspect of contagious yawning is its correlation with empathy. Multiple studies have shown that people with higher empathy are more likely to experience contagious yawning.

Several pieces of evidence support this hypothesis. First, individuals with autism spectrum disorder (ASD) tend to show a lower frequency of contagious yawning. Since ASD is characterized by difficulties in social cognition and empathy, the reduced contagious yawning suggests a link to empathy mechanisms. Second, individuals with high psychopathy traits have also been reported to show less contagious yawning. Third, yawns from closer acquaintances are more contagious. An Italian research team demonstrated that contagion rates decrease in the order of family > friends > acquaintances > strangers.

3. The Social Synchronization Hypothesis

From an evolutionary perspective, contagious yawning may have functioned as a mechanism for synchronizing group behavior. If yawning serves as brain cooling (i.e., arousal regulation), then the spread of yawning within a group would synchronize the arousal levels of the entire group. During the hunter-gatherer era, having group members become alert at the same time and rest at the same time would have been a survival advantage. It would have optimized sentry-and-sleep rotations and the group's overall vigilance.

Surprising Facts About Yawning

Fetuses Yawn Too

Ultrasound imaging has confirmed that fetuses yawn as early as 11 weeks of gestation. Since fetal yawning cannot be "contagious," this demonstrates that yawning itself has a physiological mechanism independent of social function. Contagious yawning is thought to be a layer of social cognition built on top of this basic physiological response.

Yawning Is Contagious Just by Reading About It

Have you felt the urge to yawn while reading this article? In fact, yawning is contagious not only by seeing it visually but also simply by reading the word "yawn" or even just thinking about yawning. This means that contagious yawning involves higher-order cognitive processes (activation at the conceptual level) rather than simple visual imitation.

Dogs Empathize with Human Yawns

Multiple studies have confirmed that dogs exhibit contagious yawning in response to human yawns. Furthermore, dogs respond more strongly to their owner's yawns than to those of strangers. This has attracted attention as evidence of a cross-species empathic bond between dogs and humans. Over approximately 15,000 years of domestication, dogs have developed the ability to read human social signals. (Books on animal cognition are also a helpful reference.)

Summary

Contagious yawning is a complex phenomenon in which multiple social cognitive mechanisms - mirror neurons, empathy, and social synchronization - are layered on top of the physiological function of brain cooling. People who are more susceptible to contagious yawning are likely those with higher empathy. The next time someone's yawn spreads to you, consider it evidence that your brain is automatically sensing and resonating with another person's state. Yawning is a small mirror reflecting human sociality.