Tuesday, February 11, 2014

Pass me a "YAWN" and I'll knit you a sweater

By: Brett Vassar



Why do we yawn? More importantly, why is yawning contagious? Why does simply seeing someone yawn or even thinking about yawning make you want to yawn? Have you yawned yet? First off, let’s go through some hypotheses of why people may yawn in the first place. I’m sure we have all heard the idea that we yawn because we are trying to obtain more air, or oxygen, for our brain and body. 

Well, I hate to burst your bubble, but studies have shown that no matter how much oxygen is in the air around a person, they aren’t more or less likely to yawn (Provine et al., 1987). Similarly, when exercising, when the body really needs more oxygen, people do not yawn more frequently than when at rest (Provine et al., 1987).

You may be thinking, “whoa Brett, where are you coming up with all this 'low oxygen levels makes me yawn' shenanigans, I yawn when I’m sleepy”.  Well, you are correct, sort of. While many of us yawn early in the morning or late at night, or even in the middle of class (usually when the professor is looking straight at you), it may be because we are tired or bored, but there hasn’t been enough research done to definitively say that we yawn because we are tired.

So, what does make us yawn so much? One of the leading hypotheses that research has supported to date has to do with keeping it cool; your brain, that is. 

Gallup and Gallup, 2007
When your brain is exhausted and tired, your internal brain temperature increases, but your brain has very specific temperatures at which it optimally operates; therefore when you yawn, bringing in outside air through your mouth may help cool your facial blood, which helps cool your brain down, thus make you more alert (Gallup and Gallup, 2007). Does this hypothesis point towards yawning as a physiological mechanism for brain thermoregulation? It's possible. To get a better idea of brain thermoregulation through yawning the phenomenon of contagious yawning (yawning in response to observing/hearing another yawn) comes into play (more detail later on). Gallup and Gallup (2007) used contagious yawning to study how yawning may be a mechanism in which humans cool the brain down. In their study, they had subjects watch a video of people yawning while either placing a cold pack on their forehead, a warm pack on their forehead, or sitting at room temperature and counting the number of times they yawned. Their data show that when a cold pack is placed upon the forehead people are less susceptible to contagious yawning compared to when at room temperature or when a warm pack is held against the forehead (Temperature Experiment Figure). Crazy right?! What really is yawning all about? These are just a few of the hypotheses that have been shot down, generally “accepted”, and scientifically supported.


Now, why is YAWWWWWNING so contagious? Did I get you there? The answer lies within two mechanisms; a) the empathy model and b) the mirror neuron system.

a) The empathy model

For empathy, contagious yawning is thought to be a primitive expression involved in self-awareness and "theory of mind", or the ability to want to empathize with and infer what others want, know, or intend to do (Platek et al., 2005). Therefore, seeing or hearing someone else yawn may act as a stimulus that activates neurological signals that initiate yawning (Platek et al., 2005). Functional Magnetic Resonance Imaging (fMRI) showed that parts of the brain involved in empathy “lit up” in response to contagious yawning (Platek et al., 2005). These areas included the posterior cingulate (Platek et al., 2005), superior temporal sulcus (Schurmann et al., 2005), and the ventromedial prefrontal cortex (Nahab et al., 2009) (Seen in the figure below; dark gray areas).
Guggisberg et al., 2010

Giganti and Ziello, 2009
Taking into account the link between contagious yawning and empathy, some researchers hypothesized that the effect of contagious yawning would be impaired in people with disorders in social interaction. Therefore, children with autism who exhibit impaired social interactions yawn less frequently than other children without autism when viewing videos of other people yawning (Giganti and Ziello, 2009). The figure on the right shows that typically developing children (T.D.; without autism) yawn more frequently to yawning videos than higher functioning autistic children (H.F.A.), and those higher functioning autistic children yawn more frequently to those videos than lower functioning autistic children (L.F.A.) (Giganti and Ziello, 2009). Contagious yawning has also been shown to begin occurring around the age of five, at the point when children begin to develop the ability to identify other’s emotions properly (Guggisberg et al., 2010).

Also, yawn ‘contagiousness’ has been shown to be more contagious when viewing someone you can empathize more with (i.e. family and friends). Therefore, one is more susceptible to a contagious yawn from family (3) or friends (2), than from acquaintances (1) or strangers (0) (Norscia and Palagi, 2011).
Norscia and Palagi, 2011

b) The mirror neuron system.

Mirror neurons are a type of visuomotor neuron (involved in vision and movement) that are excited during the execution of certain actions, as well as when hearing or seeing corresponding actions being performed by others (Keysers, 1982). Mirror neurons were first discovered in macaque monkeys when neurons in the F5 region of the premotor cortex (inferior frontal gyrus) fired in response to performing a specific action, as well as when observing another individual performing that same action (either human or monkey) (Rizzolatti and Craighero, 2004).

Guggisberg et al., 2010

In humans, the mirror neuron system has been shown to be important in understanding actions and imitations of others, and specifically, mirror neurons located in the posterior inferior frontal (Figure to left; light gray area, pIFG ) gyrus of humans seem to be activated by contagious yawning (Rizzolatti and Craighero, 2004). Mirror neurons are known to be involved in a model known as non-conscious mimicry or “the chameleon affect”, which occurs when you imitate someone else’s behavior without noticing it (Iacoboni, 2009). So we may yawn because we are unconsciously copying someone’s behavior. Research has shown that the mirror neuron system plays an important role in this non-conscious mimicry model (Iacoboni, 2009). fMRI studies have shown that when we see someone yawn or even hear there yawn, mirror neurons tend to “light up”, causing us to perform that same action (i.e. the yawn) (Haker et al., 2013).
Haker et al., 2013

So, how many times did you yawn while reading this blog? 1? 2? 3? 10? (Hopefully it wasn't because this blog was a snoozer). The next time you’re yawning in class or while pulling an all nighter finishing your osmoregulation paper, think about the reason why you might be yawning… Are you trying to cool your brain down to make yourself more alert? Are you contagiously yawning due to empathy? If so, how close are you with this person? Is this person a family member, friend, acquaintance, or stranger? Or could you simply be activating mirror neurons in your brain in response to observing the action of yawning? Either way, keep on yawning!

Are cats contagious yawners?

Enjoy this video of cute animals yawning!


Gallup, A.C., G.G. Gallup 2007. Yawning as a Brain Cooling Mechanism : Nasal Breathing and Forehead Cooling Diminish the Incidence of Contagious Yawning. Evolutionary Psychology 5:92–101.

Giganti, F., and M.E. Ziello. 2009. Contagious and spontaneous yawning in autistic and typically developing children. Current Psychology Letters 25:1–11.

Guggisberg, A. G., J. Mathis, A. Schnider, and C.W. Hess. 2010. Why do we yawn? Neuroscience & Biobehavioral Reviews 34:1267–1276.

Haker, H., W. Kawohl, U. Herwig, and W. Rössler. 2013. Mirror neuron activity during contagious yawning-an fMRI study. Brain Imaging Behavior 7:28–34.

Iacoboni, M. 2009. Neurobiology of imitation. Current Opinion in Neurobiology 19: 661–665.

Keysers, C. 1982. Quick guide Mirror neurons. 971–973.

Nahab, F.B., N. Hattori, Z.S. Saad, and M. Hallet. 2009. Contagious yawning and the frontal lobe: An fMRI study. Human Brain Mapping 30:1744-1751.

Norscia, I., and E. Palagi. 2011. Yawn contagion and empathy in Homo sapiens. PLoS One 6:e28472.

Platek, S. M., F.B. Mohamed, and G.G. Gallup. 2005. Contagious yawning and the brain. Brain Research. Cognitive Brain Research 23:448–452.

Provine, R.R., B.C. Tate, and L.L. Geldmacher. 1987. Yawning: no effect of 3-5% CO2, 100% O2, and exercise. Behavioral Neural Biology 48:382-393.

Rizzolatti, G., and L. Craighero. 2004. The mirror-neuron system. Annual Review of Neuroscience 27:169–92.

 Schurmann, M., M.D. Hesse, K.E. Stephan, M. Saarela, K. Zilles, R. Hari, and G.R. Fink 2005. Yearning to yawn: The neural basis of contagious yawning. NeuroImage 24:1260-1264.

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