Today as I was riding home from campus on the bus, I was talking on the phone, and my interlocutor yawned. Almost immediately, I yawned as well. She made a joke about it, and I said that it wasn't my fault, because yawning is contagious -- when you see or hear someone yawn, you tend to yawn as well. I thought that was a well-known fact, but apparently she had never heard it, or noticed it before, so my first instinct was to prove that it was true by explaining to her why it happened. Then I realized that I had no idea why it happened. So I decided that when I got home, I would look it up. Let it never be said that I am not a geek.
So, I got home and started researching the topic, and quickly discovered that I was not alone. It seems that nobody's sure why yawning is contagious. There do appear to be some differences in individuals who are susceptible to contagious yawning and those who are not1. In particular, contagious yawners score lower on the Schizotypal Personality Questionnaire, which was designed to measure the symptoms of Schizotypal Personality Disorder. These symptoms involve less social and self-awareness, along with schizophrenia-like symptoms such as altered or unusual perceptions, particularly in social contexts, which can lead to paranoia. Lower scores on the test indicate lower levels of schizotypal symptoms. Contagious yawners also performed better when answering questions about stories designed to test for theory-of-mind ability. Finally, they also had much faster reaction times when asked to identify their own face presented on a computer screen. Steven Platek and his co-authors argue that these findings, that contagious yawners score lower on the Schizotypal Personality Questionnaire, and show better theory-of-mind and self-recognition performance, indicates that self-awareness and empathy underlie contagious yawning.
This would fit with what we do know, and can easily see about contagious yawning: it is automatic and unconscious. We don't try to yawn when we see or hear someone else do so; we just do. Self-recognition and theory-of-mind mechanisms are generally fast, automatic, and unconscious, and thus it is plausible, given the data described above, that they are involved in contagious yawning. But the data I described above is pretty thin, and is certainly open to alternative interpretations. To find out for sure, I looked to neuroscience. Unfortunately, when I got there, the picture got a bit muddier. In a very recent study (published in February), researchers had participants watch videos of yawning while they were scanned using functional magnetic resonance imaging (fMRI)2. They found that people who watched the yawning videos had increased activation in the right posterior superior temporal sulcus and in the anterior superior temporal sulcus in both hemispheres. These areas are associated with the processing of social information, and the increased activation in these areas thus fits with the theory that social awareness may underlie contagious yawning. However, they did not find activation in Broca's area, which is thought to house the human version of the mirror neuron system, and believed to be associated with theory of mind. Furthermore, they found that participants who watched the yawning videos showed decreased activation in the left periamygdalar region. This area of the brain is associated with the recognition of emotional facial expressions.
These last two findings are confusing, and perhaps inconsistent with Platek's theory. It appears that, while social information processing does underlie contagious yawning, action and emotion recognition, which are parts of our theory-of-mind abilities, are not associated with contagious yawning. However, to make things even more confusing, Platek and his colleagues have conducted their own imaging study3. When contrasted with laughing and neutral videos, yawning videos caused increased activation in the posterior cingulate and precuneus, areas associated with, among other things, autobiographical memory, emotion, and self-judgements. Thus, Platek's findings are consistent with his theory, but inconsistent with the only other imaging study of contagious yawning.
The take home message, then, is that it's not quite clear what causes contagious yawning. Sure, we can say with a high degree of certainty that social-information processing is involved, but that seems obvious. What's less obvious is what else is involved. Are empathy and self-awareness involved? The neuroimaging data is too inconsistent to say for sure.
However, if it turns out that empathy and self-awareness are involved in contagious yawning, then another finding becomes much more interesting. It was previously thought that, while yawning occurs in many animal species, only humans yawned contagiously. It turns out, chimps may yawn contagiously as well. James Anderson and his colleagues published a paper in late 2004 in which they presented six adult female chimpanzees with videos depicting facial expressions, including yawning. When the videos showed yawning, two of the six chimps yawned more frequently than when watching other expressions4. While this is obviously a preliminary finding, if it turns out that chimps do yawn contagiously, and that contagious yawning requires empathy and self-awareness, as Platek argues, then we would have strong evidence that chimps are self aware and have some level of theory-of-mind/empathy.
1Platek, S.M., Critton, S.R., Myers, T.E., & Gallup, G.G., Jr. (in press, 2003). Contagious yawning: The role of self-awareness and mental state attribution. Cognitive Brain Research, 17(2):223-7.
2Schurmann, M., Hesse, M..D, Stephan, K.E., Saarela, M., Zilles, K., Hari, R., & Fink, G.R. (2005). Yearning to yawn: the neural basis of contagious yawning. Neuroimage, 24(4), 1260-1264.
3 Platek, S.M., Mohamed, F.B., & Gallup, G.G. Jr. (In Press). Contagious yawning and the brain. Cognitive Brain Research.
4Anderson, J.R., Myowa-Yamakoshi, M., & Matsuzawa, T. (2004). Contagious yawning in chimpanzees. Proceedings of the Royal Society: Biological Sciences, 271, Biology Letters Supplement 6, S468 - S470.