We all know we yawn when we are sleepy or bored. But we also yawn because we’re stressed, not just when we are tired.
Robert Provine, a neuroscientist and author of Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond, believes yawning is a displacement activity. Displacement activities are unexpected and often unintended behaviors which happen when two conflicting emotions are present – such as fear and aggression. There are many examples of displacement activities in humans; two common ones are stroking a non-existent beard and repeatedly tugging on an earlobe.
Research suggests we yawn to regulate the temperature of our brain, particularly when trying to cool off. After spending an extended period outside, people yawn more in the summer than in the winter. According to Professor Gallup, the deep inhalation associated with yawning floods air into our nasal and oral cavities, cooling the cranial arteries. In addition, opening our mouths widely increases circulation to our skulls, forcing warm blood out of the brain. Essentially, yawning reduces the temperature of the brain.
While it’s a small sample size, Professor Gallup demonstrated this cooling effect in rats. He found that even very small increases in temperature (0.18 degrees F) triggered yawns. In addition, skull temperature fell after the rats yawned — supporting the theory that yawning cools the brain.
So why do we yawn when we’re stressed?
Stress and anxiety trigger our bodies to produce increased cortisol in the blood which in turn causes our brains to get hotter. According to Professor Thompson, this stimulates the production of adrenaline to make us more alert and also tells the hypothalamus to cool down the brain. The hypothalamus acts like a thermometer for the body and, among other things, leads to yawning.
The relationship between stress and yawning has been shown in multiple animal studies. Japanese researchers used classic fear conditioning to induce yawning in rats. In another study, male Siamese fighting fish yawned multiple times during different aggressive encounters with one another. And macaques yawn in response to threats and sexual jealousy.
So, the next time you’re a hot head and want to calm down, the best approach might be to literally cool down. Sit in front of the air conditioning or go outside if it’s during cold weather. Take a cold shower or a dip in a pool. Or simply yawn a few times.
If you’re stressed, it’s a good idea to yawn.