I’ve written here before about yawning and how it’s physiological purpose continues to stump scientists.
One leading theory has been that yawning helps send oxygen to the brain, perhaps to counter excess carbon dioxide, which is a waste product that can accumulate in our bodies when we’re tired or sleepy and, thus, more likely to be breathing slowly and shallowly. (We get rid of carbon dioxide, of course, when we exhale.)
But no study has been able to show that yawning and blood oxygen levels are connected.
More recently, scientists have proposed that yawning helps cool the brain to keep it at a temperature that maximizes alertness and efficiency. Studies involving both rats and people have found, for example, that brain temperature rises sporadically before a yawn — and falls again immediately afterward. Research has also shown that human brains tend to heat up when we are in need of sleep and/or are physically tired.
A new study, published last week in the journal Physiology & Behavior, adds more evidence in support of this yawning-as-brain-cooling-mechanism theory. The study found that the amount of yawning people do is dependent on the temperature of the air around them.
A tale of two cities
For the study, researchers approached 120 people walking outside in Vienna, Austria, during both winter and summer months. The pedestrians were shown 18 photos of other people yawning and were then observed to see if and how often they yawned while looking at the photos. They were also asked questions about how long they had been outside before participating in the study, how long they had slept the night before and how old they were.
The results of this study were then compared to an identical one conducted previously in Tucson, Arizona. The researchers found that the people in Vienna yawned more in summer than in winter, while those in Tucson yawned more in winter than in summer.
It didn’t matter, then, what season it was. Nor did it matter how long or short the days were. In both locations, contagious yawning was most likely to occur during a temperature “Goldilocks zone” of around 68 degrees Farenheit.
In other words, the participants were most likely to yawn when the temperature was neither too hot nor too cold.
Unnecessary at both extremes
That finding actually fits the yawning-cools-the-brain hypothesis. For, as the authors of the study explain, yawning may not be necessary when ambient temperatures get too cold. And when temps get too hot, yawning may simply not work at cooling the brain, so we tend to not yawn as much then, either.
But when ambient temperatures begin to get slightly warmer than the brain, a yawn may help us keep our cool, so to speak — and keep us alert. And by “spreading” the yawning to those around us, we ensure (evolutionarily speaking) that our social group stays vigilant, too.
At least, that’s the theory.
If you live here in Minnesota, you can test the theory yourself today. We may reach that yawning “Goldilocks zone” of upper 60s around noon.