Yawning: The Long Stretch

Why do we know so little about something we do more or less every day? It’s a widespread activity which gives us enormous pleasure and biological satisfaction. Dogs do it. Chimpanzees do it. Even babies in the womb do it. What is it? I’m referring to the everyday act of yawning. Even scientist are not in total agreement about the process, and argue about its function. Everyone knows that yawning is contagious. If someone yawns at the dinner table others are likely to follow suit. Even reading this article will make many of you mimic the activity I’m describing. Scientists in Japan have found that a third of adult chimps will yawn if they’re shown a video of other chimps yawning. A recent learned article in the New Scientist magazine claimed that contagious laughter only occurred in meat eating animals, but several readers were quick to write to the editor saying that it was also seen in herbivores such as deer, horses, sheep and alpacas.

We yawn when we’re bored and also when we’re tired. This led our parents to believe that yawning was a fatigue signal: a sure sign that people were ready to drop off to sleep. This theory was supported by the observation that surgical patients tend to yawn when they’re going under an anaesthetic. But now the consensus of scientific opinion has done a complete U-turn. Today it’s believed that we yawn, not as a prelude to sleep, but when we want to attain a state of greater alertness. Paratroopers tend to yawn just before they jump. At that critical point they take in gulps of air to increase their level of arousal. The yawns signal the transition from the boredom of the flight to the alertness needed for the descent. One theory is that we yawn in order to cool the brain and help it work more efficiently. Breathing deeply, whether through the mouth, or through the nose, is known to cool the blood travelling to the brain. To examine the importance of this mechanism two psychologists from the State University of New York carried out an ingenious experiment. They exposed volunteers to videos of people yawning, and found that half were provoked to follow suit. But when they held a cold pack to their forehead to chill their brains, none of the subjects showed any signs of contagious yawning.

Hippocrates, the father of modern medicine, thought that human beings yawned to draw in more of the vital life force, which was then called spiritus. When they did so they felt ‘inspired’, just as the modern takers of recreational ‘uppers’ do when they take psychedelic drugs. This accords with the findings of psychological research, when people have been asked to rate a variety of pleasurable experiences on a scale ranging from nought to ten. The results placed yawning high on the list of cheerful activities, with a rating of 8.5 on the ten point hedonic scale. Further support for the arousal function of yawning is that the forceful opening of the mouth, and sharp intake of air, is often associated with stretching of the arms, a movement officially known as pendiculation. Ultrasound studies of three- month old foetuses in the womb show that at this stage of their development they begin to yawn, and at the same time stretch their limbs. These are the movements that cats make after a long snooze when they yawn and stretch their limbs to prepare themselves for the day’s activities. This activity is almost certainly hard-wired into our brains, because when people suffer a stroke, and are paralysed on one side, they’re often surprised to find that their bad arm makes an involuntary movement when they yawn. So let’s not stifle our yawns. Instead let’s draw full benefit from their cheering and energising effect.

Key words: Yawning, Contagious yawning, Brain temperature.

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