Why do we yawn? Nothing to do with boredom - we're just cooling our brains, say scientists


James Vincent
Monday 12 May 2014 13:39 BST

A new study has suggested that the reason we yawn has nothing to do with tiredness or boredom, but actually works in order to cool down our brains and help us think a little clearer.

Like any computer the brain has an optimal working temperature and when it becomes too hot yawning helps cool it down, increasing both the heart rate and blood flow while delivering a big gulp of air to the head, cooling the blood in that area.

Previously it’s been thought that yawning served a respiratory function, helping to wake us up with a jolt of oxygen when we were feeling sluggish, but studies have shown that yawning doesn’t actually increase oxygen levels in the body; something that tallies with the simple observation that we don’t yawn when we exercise, a time when we definitely need more oxygen.

So why do we yawn when we’re tired? Well, both sleep deprivation and exhaustion are known to increase brain temperature, so while it’s true that we yawn to combat lack of sleep, yawns don't make us ‘more awake’ but instead help keep our brains operating at the right temperature.

Yawning isn't limited to humans - most animals with a spine yawn.

Researchers from the University of Vienna observed pedestrians’ yawning habits in both Austria and the US and found that contagious yawning was most frequent in a ‘thermal window’ when it was cold enough outside for the yawned air to cool the body down, but not so cold (or so hot) that the air would have harmful consequences. This meant that citizens in sweltering Arizona yawned more in winter while in chilly Vienna they yawned more in summer.

The research, published this May, tallies with a number of previous studies such as one from the University of Albany that found that contagious yawning could be directly influenced using hot and cold packs. Researchers found that subjects watching a video of people yawning were 41 per cent likely to yawn themselves when holding warm pack to their head, but only nine per cent likely to yawn when holding a cold pack.

This theory of yawning-as-thermoregulation also tallies with explanations of the behaviour as ‘positively contagious’; aka a herd behaviour that helps keep every member of the group alert, as well as having the beneficial side effect of stretching out bodies to keep them limber (word fact: yawning accompanied by stretching is known as ‘pandiculation’).

Our susceptibility to contagious yawning is also affected by our capacity for empathy. Studies have shown that contagious yawning first begins in children at the same age as they learn to identify others’ emotions (about 4 to 5 years old) and that children with autism (a neural condition that impairs social interaction) are less likely to yawn when shown videos of others yawning.

Yawning is so contagious that we only need to read about it to want to yawn ourselves. In fact, you’ve probably yawned at least once since reading this article. At least we know that that’s not because you’re bored – in fact, thanks to the yawning and your newly-cooled brain, you’re probably more alert than you were before.

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