Yawning Helps Cool the Brain Say Scientists

Posted on May 11, 2014

Researchers from the University of Vienna, Austria, and the Nova Southeastern University and SUNY College at Oneonta, USA say the function of yawning is to cool the bran. The study was led by SUNY Oneonta Assistant Professor of Psychology Andrew Gallup. Gallup's team measured contagious yawning frequencies of pedestrians outdoors in Vienna, Austria, during both the winter and summer months. They compared the results to an identical study in Tucson, Arizona. In both studies contagious yawning frequencies were higher in certain temperature ranges and less frequent at temperature extremes.

Gallup's theory on yawning as a brain cooling mechanism is called the thermoregulatory theory. According to the theory "yawning functions to cool the brain, in part, due to the heat exchange that happens as we stretch the jaw and take a deep inhalation of air."

A research paper, published here in Physiology & Behavior, says the study found that yawn frequency increases in the summer.
As predicted, the proportion of pedestrians reporting yawning was significantly lower during winter than in summer (18.3% vs. 41.7%), with temperature being the only significant predictor of these differences across seasons. The underlying mechanism for yawning in humans, both spontaneous and contagious, appears to be involved in brain thermoregulation.
A press release about the study says contagious yawning was constrained to an optimal thermal zone or range of ambient temperatures around 20 degrees Celsius (68 degrees Fahrenheit). If yawning does help cool the brain it would not be as useful when the weather is too hot and it could be harmful if it is cold. Lead author Jorg Massen of the University of Vienna says "yawning is not functional when ambient temperatures are as hot as the body, and may not be necessary or may even have harmful consequences when it is freezing outside."

The researchers also say that previous research has failed to show an association between yawning and blood oxygen levels, which disputes a common belief that yawning helps increase oxygen supply to the brain. CNN reports that other factors in the study, even lack of sleep, did not have a significant impact on a person's yawning.