Why do we yawn and why is yawning contagious?

Why write an intro when you can start with a video involving a baby sloth?

Has this ever happened to you: You’re talking to someone, you’re feeling very energetic and awake. The other person yawns. You start yawning too.

In fact, by the time you finish reading this, I guarantee you’ll probably have yawned at least once… Although, now that I’ve told you you will, maybe you won’t.

Let’s start with what happens to our bodies when we yawn. It starts with opening our mouths. Wiiiiiiide. Breathing in deeeeeply.

Sidenote: I find the wider and bigger the yawn, the more satisfying.

Anyway, wiiiideee, biiiiiiiggggg… Many parts of your body are in full action when you yawn. Think of all the muscles it takes to open your mouth (at least 12). You breathe in deeply while your lungs fill with air and expaaaaaaaaand.  While your lungs expand, your abdominal muscles are flexed and you’re pushing your diaphragm down.  Whooooaaaaa. Who would have thought that our bodies do that many things while yawning. What’s more, yawning has been found to be involuntary. Uncontrollable. In fact, we yawn before we’re even born. Yup. According to the research of neuroscientist Robert Provine, a yawning expert (yes, you read correctly – a yawning expert!!), 11-week old fetuses yawn. Double-whoooa.

So,  why do we yawn?

The common assumption is that you yawn when you’re tired or bored…or when you are super relaxed. But, that may not necessarily be true. According to Robert Provine, yawning could also signal that you’re totally alert or that you are sexually aroused. Hmm…that doesn’t sounds right, does it – but let’s get back to that later.

One of the first theories for yawning can be traced back to the father of medicine, Hippocrates. He said that yawning normally precedes a fever and is used to remove bad air from the lungs. Other early medical studies suggested similar reasons for yawning, i.e. to increase our blood pressure, heart rate and oxygen in the blood, helping the body and brain to improve motor function and alterness. But, experiments have shown that people subjected to increased CO2 levels did not yawn more frequently. Similarly, an increase of O2 had no impact on yawning rates (Provine et al, 2000). Sorry, Hippocrates.

One of the most recent studies on yawning says that we yawn to prevent our brain from overheating. Gary Hack and Andrew Gallup of Maryland and Binghampton University argue that yawning causes the walls of our sinuses to expand and contract, pumping air into the brain and therefore lowering its temperature. Sinuses are cavities in the human head and their existence is apparently also “baffling” to scientists…I think, “normal” people and scientists may perhaps have different definitions of the word “baffling”. Anyway, to put it more simply, the human brain is sensitive to temperature and, like a computer, doesn’t work well if it overheats (Gallup, Medical Hypotheses, 2008). That’s why this theory is also called the “brain-cooling hypothesis”.

“Based on the brain-cooling hypothesis, we suggest that there should be a thermal window in which yawning should occur. For instance, yawning should not occur when ambient temperatures exceed body temperature, as taking a deep inhalation of warm air would be counterproductive. In addition, yawning when it is extremely cold may be maladaptive, as this may send unusually cold air to the brain, which may produce a thermal shock”, says Gallup. To test the hypothesis, Gallup and his colleagues studied wild parakeets (chosen because they have large brains for their size and because they are subject to frequent temperature changes). In their experiments they subjected different groups of birds to frequent changes in ambient temperature (22° – 38° degrees celsius) and found that the birds were more than twice as likely to yawn when temperature rises occured. In fact, yawning behaviour peaked at 30 degrees celsius and then decreased.

Ok ok, we’re not birds. So could this really apply to us? Well, Gallup also studied two women who suffered from chronic bouts of yawning from 5-45 minutes in length, occuring up to 15 times a day. He found that both women seemed to have dysfunctional brain temperature regulation disorders. And what’s more, after they adopted certain oral exercises (get your mind out of the gutter), they reported a decrease in the occurence of yawning bouts.

However, there is still not enough evidence to really prove  the thermoregulatory function of yawning. Two other popular studies suggest that yawning is either a sign of arousal or sleepiness. Let’s call them the sexy theory and the sleepy theory.

The sexy theory says that yawning can trigger the release of dopamine in the brain which can have a domino effect on other brain chemicals such as oxytocin and nitric oxide (that’s the sexy stuff that erections are made of). Moreover, when scientists experimented with the drug PT-141 or melanotan (a skin tanning agent) they also found that the in addition to causing erections, the drug also induced yawning…and nausea. Hmm….erections, yawning and nausea. What a sexy combination. Of course, this all sounds very circumstantial, but many researchers are convinced there is a link between sexual arousal and yawning. Provine puts it this way: Yawning is associated with a shift of state or behaviour, including from not being aroused to being aroused. He also believes that yawning and sexual climax may share neurobehavioural heritage. Might explain why yawning is so satisfying.

However, the sleepy theory is much more common. Some studies have shown that yawning actually lowers arousal levels (Deputte, 1994) and that decreasing wakefulness has been found after yawning. Moreover, from self-observation, most people will probably admit that they are more likely to yawn when they are tired.

So, to sum up. Why do we yawn – no one really knows for sure. It may have something to do with your brain or being more or less alert, but no one has a definite answer for physiological reasons of yawning.

So, let’s move on to much more interesting question- Why is yawning contagious?

Seems like yawning is more than just something we “do”. Many studies suggest that the contagiousness of yawning may depend on our social competence and is often linked to empathic skills in healthy human beings. Experiments have shown that people with autism, schizophrenia or other disorders that affect social interactions, are much less likely to be susceptible to contagious yawning (Lehmann, 1978, Haker and Rossler, 2009).

“Watching or hearing other persons yawn activates a complex network of brain regions related to motor imitation, empathy, and social behaviour…In monkeys, the contagiousness of yawning correlates with the level of grooming contact between individuals, i.e. it is higher in animals that are socially and emotionally close to each other”(Guggisberg et al, 2010).

And these findings are in line with what neurologists found in brain imaging: Contagious yawning is associated with the same areas of the brain that deal with empathy (the precuneus and posterior temporal gyrus, at the back of the brain).

But there are other theories, saying that we’ve adopted yawning as a communication channel, an unconscious “herding behaviour”, a subtle way to communicate to those around us how we feel or how alert we are. Therefore, yawning can often signal boredom or sleepiness. You subconciously tell people “I’m not interested in what you’re saying” or “Hey – I’m tired” (Go figure). Some researchers also believe yawning goes back to our primitive stages when we didn’t have language to signal to our tribe members that it was time to go to sleep or to wake up, or to signal that we trusted them enough to let our guards down.

So, whether physiological or social…yawning is not so boring after all.

I think I have yawned about 15 times since I’ve started writing this. Have you yawned yet? If you haven’t, you are a medical aberration. I hope you know that.


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