The phenomenon of contagious yawning has been analyzed by researchers for many years. Though many believe yawning increases oxygen supply to the brain, researchers publishing in Physiology & Behavior have concluded that the purpose of yawning is to cool the brain.

The team, led by Andrew Gallup of SUNY College at Oneonta, NY, notes that previous research into the subject has not been able to produce a link between yawning and blood oxygen levels.

They say that changes in brain temperature are linked with sleep cycles, cortical arousal and stress. As such, they theorized that yawning could also be affected by surrounding variations in temperature and that exchanging cool air via yawns could lower brain temperature, achieving “optimal homeostasis.”

In detail, they predicted that yawning would only occur within a “thermal window” – that is, within an optimal span of temperatures.

Though previous research has shown that frequency of yawning decreases as ambient temperatures increase and approach body temperature, the team says “a lower bound to the thermal window has not been demonstrated.”

To investigate further, Jorg Massen and Kim Dusch, of the University of Vienna in Austria, gauged the frequency of contagious yawning in pedestrians walking around outside in Vienna during both winter and summer months.

They then compared their results with a corresponding study conducted in the dry climate of Arizona.