Why is yawning contagious?

Why is it that we often have an uncontrollable urge to yawn when we see someone else yawning? It happens all the time, but most of us have no idea why we do it – it occurs completely automatically. Interestingly, this phenomenon doesn’t just occur in humans, it has been shown in primates too (Anderson et al, 2004) as well as other animals. Maybe yawns signify more than just tiredness.

To start off, it might be useful to explore what’s going on in the brain when we experience a contagious yawn. One hypothesis is that contagious yawning is linked to excitability (in terms of higher activity) in the motor cortex, with people who have more excitability showing higher levels of yawning when shown stimuli of people yawning (Brown et al, 2017). Other imaging studies have explored the patterns of brain activity during contagious yawning, and found evidence to suggest that a part of the motor cortex containing mirror neurons is important for this action to happen (Haker et al, 2013). Mirror neurons, as the name suggests, are active when we carry out an action, or when we see others carry out the same action (to find out more click here).

One well-known theory for yawning contagion is that we yawn to show empathy. Evidence to support this has come from several studies, for example one study found that children with autism (thought by some to have lower levels of empathy) yawned less than their peers when they were shown videos showing people yawning (Senju et al, 2007). Similar findings have also been shown in participants with schizophrenic traits, a condition also linked to low empathy (Platek et al, 2003). And remember the mirror neurons described above? They are also thought to be linked to empathy as they are involved in aspects of social communication (Gallese, 2007). However, not everyone agrees – one recent review described the current evidence as ‘inconsistent and inconclusive’ (Massen & Gallup, 2017), suggesting that more research needs to be done before a link can be made. For example, they suggest that children with autism yawn less when shown these stimuli because they don’t focus as much on faces, which could explain the finding described above.

An alternative theory is that yawning has a more functional advantage: it is used to cool down our brains. Breathing in a large amount of air is enough to cool the blood in the face, which in turn cools down our brain. For example, one study found that participants recorded contagious yawning more in summer (when temperatures were higher) than in winter (Massen et al, 2014).

Yawning is also thought to be linked with improving focus. Waluskinski (2014) hypothesises that the physical act of yawning helps to increase the circulation of cerebrospinal fluid, which in turn helps to clear any sleep-inducing hormones from the brain. Contagious yawning could therefore be evolutionary advantagious. For example, if one member of a pack yawns, it causes others to do the same, therefore keeping the whole pack alert and on the look out for predators or prey.

Thank you for reading, and thanks to Bex for suggesting this post! If there’s anything else you’d like me to write about then let me know in the comments below.

References:

Anderson, J. R., Myowa-Yamakoshi, M., & Matsuzawa, T., 2004. Contagious yawning in chimpanzees. Proceedings. Biological sciences, 271 Suppl 6(Suppl 6), S468-70.

Brown, B.J., Kim, S., Saunders, H., Bachmann, C., Thompson, J., Ropar, D., Jackson, S.R. and Jackson, G.M., 2017. A neural basis for contagious yawning. Current Biology, 27(17), pp.2713-2717.

Gallese, V., 2007. Before and below ‘theory of mind’: embodied simulation and the neural correlates of social cognition. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 362(1480), pp.659-669.

Massen, J.J., Dusch, K., Eldakar, O.T. and Gallup, A.C., 2014. A thermal window for yawning in humans: yawning as a brain cooling mechanism. Physiology & behavior, 130, pp.145-148.

Massen, J.J. and Gallup, A.C., 2017. Why contagious yawning does not (yet) equate to empathy. Neuroscience & Biobehavioral Reviews, 80, pp.573-585.

Senju, A., Maeda, M., Kikuchi, Y., Hasegawa, T., Tojo, Y. and Osanai, H., 2007. Absence of contagious yawning in children with autism spectrum disorder. Biology letters, 3(6), pp.706-708.

Walusinski, O., 2014. How yawning switches the default‐mode network to the attentional network by activating the cerebrospinal fluid flow. Clinical Anatomy, 27(2), pp.201-209.

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