Yawning was earlier associated with an increase in oxygen levels in blood but a new study says it happens to cool the brain.

Researchers at the University of Vienna, Nova Southeastern University and SUNY College at Oneonta said in their study that stress levels, cortical arousal and sleep cycles are connected with fluctuations in brain temperature. Both spontaneous and contagious yawning is found to play a key role in balancing the temperatures and maintaining optimal homeostasis in brain, resulting in enhanced mental efficiency.

Researchers said that yawning does not occur during harsh cold and hot temperatures but gets triggered within an optimal range of temperatures, i.e., a thermal window

For the study, researchers observed yawning frequencies of pedestrians in Vienna, Austria, during winter and summer months. The results were then compared to the findings of a similar study conducted in Arizona. Participants were also asked to view images of people yawning and report their yawning behavior.

The researchers found that Vienna people yawned more frequently in summer than in winter, whereas Arizona residents yawned more often in winter than in summer.

The researchers also found that the frequency of the yawning did not depend on the seasons or the amount of daylight, but contagious yawning was observed within an optimal thermal zone or range of ambient temperatures around 200 C. Contagious yawning disappeared during high temperatures around 37o C in the summer of Arizona and during low or around freezing temperatures in the winter of Vienna.

Lead author Jorg Massen said that although yawning helps to calm the brain, it is not functional amid soaring temperatures and might even be harmful in freezing temperatures.

In a 2007 study, Andrew Gallup, a researcher and a yawning specialist at New York's University of Binghamton, said that yawning does not necessarily describe boredom, rudeness or fatigue.

Yawning helps the brain to cool down for an enhanced performance. Plus induces alertness and recharges a person when changing from one activity to another (sleeping to waking) to better absorb information.

"Our brains are like computers," said Gallup. "They operate most efficiently when cool. Our research indicates that we yawn in response to increased brain or body temperature," LA Times reports.