A look at the science behind yawning

To many yawning is simply a reflex that occurs when one is tired or bored. Evolutionary Neuroscientist, Andrew Gallup has been “tirelessly” studying the science behind yawning. He joins Hari Sreenivasan via Google Hangout with his insights.


To many, yawning is simply a reflex that occurs when someone is tired or bored.

Evolutionary neuroscientist Andrew Gallup has been tirelessly studying the science behind yawning.

He joins us via Google Hangout with his insights.

First, thanks for being with us.


Thanks for having me.

So what is yawning?

Why does it happen?

Well, that's a great question, and people have been asking that question for thousands of years, and it's really only within the last decade or so that we've begun to get a handle on why we yawn.

So yawning is characterized by this deep, large gaping of the mouth with a deep inhalation of air followed by a fairly rapid closure of the jaw and an expiration, and that basic motor action pattern is ubiquitous.

We see this across vertebrates.

All mammals yawn.

All birds yawn, and even fish, reptiles and amphibians show a similar yawn-type gaping pattern.

So evolutionarily, it appears to be a very highly conserved response, which suggests that it possesses some basic function.

And some of the research that we've been doing recently is trying to uncover that function, and a lot of the work that I've done is focused on the idea that yawning serves as a brain-cooling mechanism.

A brain-cooling mechanism?



So that it is one of a variety of mechanisms which could enhance blood flow to the skull, provide a mechanism for countercurrent heat exchange, which could serve to modify intracranial temperatures.

So, wait.

When I yawn, how are we talking about temperatures in my brain?

Connect the dots for me here.

Sure, so the mechanism of yawning, that gaping of the jaw and deep inhalation of air, serves to increase intracranial circulation, so it promotes blood flow to the skull, and in addition, that ambient air exchange provides a mechanism for cooling with the ambient temperature with the internal tissues of the nasal passages and the oral orifices.

Now, the cooling of this blood draining from your face then comes into close contact with the arterial blood supply in your neck and provides a mechanism to basically increase blood flow generally, removing hyperthermic blood away form the skull while simultaneously introducing cooler blood from the lungs and extremities.

Let's say your theory is right and you've explained the mechanics behind this all.

Why is yawning contagious?

So we know that contagious yawning is elicited by social stimuli.

Seeing someone else yawn, hearing someone else yawn, and even thinking about yawning could elicit the response.

So in order to understand contagious yawning, I'd argue that we first need to understand why we yawn when we're by ourselves because the motor-action pattern of contagious yawning is indistinguishable from a spontaneous yawn.


So when we yawn because we see someone else, it still elicits that same motor-action pattern, and therefore, it likely has the same physiological consequences.

So to get at the question of why we yawn contagiously, I've hypothesized that contagious yawning may be a mechanism which evolved to promote group vigilance and coordinate arousal levels among members of a group.

So if someone in the group yawns spontaneously because of, perhaps, increased brain temperature and drops in cognitive processing...


...the spreading of that response across members of the group could enhance overall vigilance.

So one of the questions that I had from Facebook, 'I've heard that yawning is a sign of empathy, and some physicians try to elicit it in children when they screen for autism.

Is this accurate?'

Yes, so there are a number of studies that have linked contagious yawning with empathy.

However, the connection isn't as tight as once believed, so there are some studies that have been conducted looking at whether or not children with autism yawn contagiously, and some of the initial studies indicated that they failed to do so.

However, this could be a consequence of just a lack of social attention towards the yawning stimulus.

Someone asks, 'I wonder why I don't see more elderly people yawn.

Maybe I just visit nursing homes at a non-yawning time or is there something to it?

I yawn more when I'm there than anyone who lives there.'

Both spontaneous and contagious yawning rates decline with age, so that elderly populations yawn considerably less than other adult populations or younger populations.

The highest frequency of yawning, in fact, occurs within the first few weeks to months following birth, so babies are the highest-frequency yawners.

I have witnessed that.

So what's the link between yawning with tiredness as opposed to boredom?

The relationship with yawning and boredom is well documented, and again, I would argue that it's tied to just dips in arousal and alertness that may be associated with increased brain temperature and lower intracranial circulation.

In relation to tiredness... So yawning is often associated with sleepiness and fatigue, but I'd argue that the connection between those two, again, is temperature, so that our body temperature varies considerably across the day in a circadian pattern, and the highest yawning rates occur at very distinct changes in our circadian temperatures, our brain and body temperatures.

So in the evening, we're more likely to yawn spontaneously than any other time in the day, and that's when our brain and body temperatures are at their highest point.

Is there a connection between yawning and how much oxygen we need?

I mean, people keep saying, 'Oh, gosh.'

Well, one person asks, 'Why do I yawn all the time?

My mom snapped at me once, 'How much oxygen do you need?''

Yeah, and so when I poll classrooms or audiences, and I ask them, 'Why do we yawn?'

the most common response is 'Oxygen deprivation,' or that we yawn to equilibrate oxygen-CO2 levels in our blood.

This is the most widely believed reason why we yawn.

However, the research has tested that, and subsequently, that hypothesis has been falsified.

So they actually brought people into the lab and had them inhale altered contents of O2 and CO2 to see its effect on yawning...


...and they find that while you can manipulate breathing rates really effectively, that yawning rates are unaffected by the manipulation of O2 or CO2.


So the connection between breathing and yawning... They're really controlled be separate mechanisms, but it's very intuitive for us to believe that yawning is associated with respiration because it has this big inhalation component.

'Do animals catch yawning as well?

My cat seems to yawn when I do and vice versa.'

There are about a handful of animals that we have very good experimental evidence for yawn contagion and maybe another half a dozen or so in which there's observational evidence for yawn contagion.

Currently, there is no evidence that cats yawn contagiously.

However, dogs have been documented... Domesticated dogs have been documented to yawn in response to human yawns.

Andrew Gallup, a yawn researcher from, and assistant professor of psychology at SUNY Polytechnic Institute, thanks so much for joining us.

Thank you so much.