New research suggests yawning frequency in humans varies with the temperature of their environment.
Most people believe yawning is a way for the body to get more oxygen, but this has never been scientifically proven, a University of Vienna news release reported.
Factors such as "sleep cycles, cortical arousal and stress" affect brain temperature, the news release reported. Yawning could be the body's way of cooling down the brain.
"Yawning should also be easily manipulated by ambient temperature variation, since exchange with cool ambient air temperature may facilitate lowering brain temperature," the news release reported.
A research team predicted yawning only occurred within a certain temperature range, or "thermal window."
To test their theory the researchers looked at contagious yawning patterns of pedestrians on the streets of cities during both the winter and the summer.
In a separate study conducted in hot United States regions such as Arizona participants were asked to look at images of people yawning and then self-report their own yawning patterns.
The European study found people in Vienna yawned more often in the summer than in the winter while people in Arizona yawned more in the winter than summer.
The researchers found yawning patterns did not rely on season or amount of daylight present, but rather a range of ambient temperatures. These temperatures were around 20 degrees Celsius (about 68 degrees Fahrenheit).
Yawning occurred less frequently when the temperature got too high (around 37 degrees Celsius) or too low.
When ambient temperatures are as warm as the body yawning is not necessary, and it could even be dangerous in frigid temperatures.
Most studies look at the interpersonal and emotional-cognitive aspects of contagious yawning; this new study suggests the function's real purpose is to regulate brain temperature.
"In turn, the cooling of the brain functions to improve arousal and mental efficiency. The authors of this study suggest that the spreading of this behavior via contagious yawning could therefore function to enhance overall group vigilance," the news release reported.
