Usually regarded as a sign of boredom and fatigue, yawning plays key role in controlling brain temperature, reports a study published in the journal Frontiers in Evolutionary Neuroscience.

When the outdoor temperature exceeds body temperature, people hardly yawn and the frequency of yawning changes with the season. The scientists Andrew Gallup, a postdoctoral research associate at Princeton University and Omar Eldakar, a postdoctoral fellow at University of Arizona’s Center for Insect Science said this seasonal disparity indicates that yawning serves as a regulatory mechanism for brain temperature.

The scientists conducted a field-observational experiment to find out the link between yawning and ambient temperature. They recorded the yawning frequency of 160 individuals in Arizona in winter and summer. The researchers observed that people yawned more frequently in winter as compared to summer when outside temperatures were lower than the body temperature. Almost 50% participant yawned in winter, as compared to less than 25% in summer.

 Dr. Gallup explained when the atmospheric air is cooler than the body temperature, inhaling it quickly cools the facial blood and brain. Also, when they analyzed data for each season separately, they noticed that length of time individuals spend outside in the climatic conditions was also related to yawning.

The same results were observed across the seasons even after they statistically controlled other features such as humidity, hours of sleep the previous night and time spent outside.

The finding also explains why tired people yawn very frequently, because exhaustion as well as sleep deprivation have been proven to increase the brain temperature. And this increased temperature prompts yawning to cool down the hot head. Past studies indicate that yawning also heightens the arousal, providing a jolt of energy in the morning.

Explaining the thermoregulatory hypothesis, which says increase in brain temperature triggers yawning, Gallup pointed that little research has been done to understand the exact mechanism and function of yawning, though many theories have been hypothesized in the past few decades, and even today there is no agreement over the purpose of yawning among the researchers studying the topic.

It’s first study that demonstrates that yawning frequency changes with season. Dr. Gallup says the research has vast applications not only in understanding the human physiology, but also in terms of diseases and disorders like epilepsy and multiple sclerosis. These diseases are generally associated with frequent yawning and thermoregulatory dysfunction.