What can yawning tell us about the brain?

Seven seconds: the average length of a human yawn. While you've probably never had the urge to time the ‘activity’ yourself, after reading this article, you may change your mind... Indeed, researchers from the psychology department at the New York State University at Oneonta had the absurd idea of comparing the length of yawns in different mammals. And they discovered a surprising connection to the brain… so what does yawning tell us?

A powerful opening of the jaw, inhalation, a brief period of intense muscular contraction and a passive closing of the jaw with a short exhalation. That’s the definition of a yawn. Although the purpose of yawning has never been clearly established, research has highlighted its role as an ‘accelerator’ and ‘ventilator.’ Yawning appears to facilitate intracranial blood circulation and cools the brain. Andrew C. Gallup and colleagues relied on previous studies supporting the neuropsychological function of yawning in order to put forward the following hypothesis; the researchers postulated that the length of a yawn is correlated with brain weight and neuron count.

To test the hypothesis, the scientists decided to time the length of yawns in animals, including humans. They relied largely on YouTube videos to obtain the data. In all, 205 yawns in 177 individuals belonging to 24 different animal species were analyzed. Among them: elephant, camel, cat, dog, gorilla, chimpanzee, fox, horse, hedgehog, mouse, rabbit, sheep, squirrel, and many others. The results of the study, published in Biology Letters, indicated that yawns tend to be longer in primates as opposed to non-primates. More precisely, humans are the longest yawners (7 seconds on average), followed by the African elephant (6 seconds), the chimpanzee, camel (4.8 seconds), gorilla, horse, lion…; squirrel, rabbit, rat, and finally mice, the shortest yawners (between 2.8 and 0.8 seconds). According to Andrew C. Gallup: “Differences in yawn duration appear to be specifically linked to interspecies variation in brain size and complexity, with cortical neuron number being the most significant factor.” Thus, bigger brains have a greater risk of overheating, requiring a longer yawn duration compared to smaller brains.

So next time you catch your coworker yawning (next Monday morning for example) be sure to time them to see who's smarter… Thankfully additional research is needed before we can confirm this type of assessment!
Source: Andrew C. Gallup, Allyson M. Church, Anthony J. Pelegrino, Yawn duration predicts brain weight and cortical neuron number in mammals, in Biology Letters, October 2016.

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