According to the The National Institutes of Health (NIH), yawning is defined as the "involuntarily opening the mouth and taking a long, deep breath of air." This most often occurs when you're feeling sleepy, experiencing a vasovagal reaction (or a stimulation of the vagus nerve), or having a brain problem (like a stroke). "Yawning can also function as a reflex to equalize air pressure in your ears. So, there is a belief that the act of yawning can actually be a form of homeostasis, or a way to maintain a stable internal physiological environment to enhance an individual's environment," Dr. Nelson says.
Why Is Yawning Contagious? A Few Theories:
While scientists have hypotheses about why yawning in front of your friend pretty much guarantees they'll yawn, too, it's important to note that none of their ideas are rock solid just yet. "While there is still much to understand about the physiology of yawning, research supports several theories regarding why we do it," says Dr. Nelson. Below, she walks you through a few theories.
1. Yawning is a form of communication high-order animals
Some researchers believe that—like nodding or shaking your head—yawning is just another form of sending a message to your fellow human beings. "There are theories that suggest that yawning is a form of communication between higher-order animals to support enhanced cognitive performance and coordination of the group by increasing oxygenated blood to the brain," says Dr. Nelson. This transmission of yawning also tends to be even more 'contagious' with loved ones compared to strangers," says Dr. Nelson.
For this reason, scientists believe that yawning may have evolved to help animals, including humans, bond with one another and make group decisions. "Functional brain scans of individuals yawning have shown increased activation in the ventromedial prefrontal cortex of the brain, which is involved in several functions, most notably, decision making," says Dr. Nelson.
2. Yawning is what's called a fixed action pattern (FAP)
FAPs are predictable actions or sequences triggered by a cue of some sort. For example, mother birds that nest on the ground have a specific, repeatable choreography that they follow if one of their eggs rolls out of the nest. Instead of each individual mama having her own take on returning the egg to safety, they are likely to perform this exact sequence. Yawning is similar.
"FAPs are typically found in lower-order animals, however humans do have a few example FAP behaviors—yawning being one of them," says Dr. Nelson. " Further, with FAPs, once they begin, they are essentially unchangeable and must be carried out to completion. Have you ever tried to stop a yawn in the middle of it?!? Yep, it can't be done! So, essentially, once a human begins to yawn, this hard-wired behavioral response must run its course."
3. Contagious yawning is a result of mirror neurons
In social mirroring, human beings (and other high-order animals) imitate the actions of those around them. For example, if I cross my arms, you might do the same. "What these neurons are involved in is matching what we sense and feel to the way we move," James Giordano, PhD, a neuroethicist and neuroscientist at Georgetown University, told PBS. "So if someone is seeing me scratch my face, they would know what it feels like. You may be compelled to do it too."
Researchers believe that human beings do this because their brains are classifying this action—be it yawning, crossing the arms, or scratching your head—as a useful action.
A Final Note on Yawning
While yawning is almost always harmless, talk to your doctor if you feel like you've been yawning more than usual. "It is common and usually is totally benign. However, if there is an increase in yawning that cannot be explained by lack of sleep or some of the other causes mentioned above, then yawning can be a symptom of some disease," says the Medical University of South Carolina.
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