New research provides more evidence that yawns function as a brain cooling mechanism. The findings appear in the journal Physiology & Behavior.

“Yawning is often misunderstood both within the scientific community and the general public,” said study author Andrew C. Gallup, an assistant professor of psychology at SUNY Polytechnic Institute.

According to the brain cooling hypothesis, yawns are triggered by rises in cranial temperature. Both spontaneous and contagious yawns function to keep the brain temperature balanced and in optimal homeostasis.

To further test this hypothesis, the researchers indirectly manipulated people’s brain temperature by having them hold a lukewarm, warm or cold compress firmly against their neck over their carotid arteries for five minutes.

The 92 participants then watched a short video depicting a random series of nine individuals yawning before completing a survey that assessed their yawning behavior and the number of hours they slept the night before.

The researchers found that the cold compress was associated with a diminished urge to yawn and reduced yawn frequency. Participants yawned significantly fewer times in the cold condition compared to both warm and lukewarm conditions.

The results are in line with a previous study conducted by Gallup and his colleagues, which found that the frequency of yawning varied with temperature of the season. Contagious yawning was constrained to a range of ambient temperatures around 20 degrees Celsius.

But the current study — like all research — include some caveats.

There were no significant differences in yawning between the warm and lukewarm conditions. However, this could be because yawning is only a compensatory cooling mechanism and the warm compress created an elevation in brain temperature that “exceeded the threshold for which yawning would be effective,” the researchers explained in their study.

To test that the experiment would actually influence brain temperature, two volunteers underwent each of the three conditions separately while being recorded by a high resolution radiometric thermal imaging camera. “While thermographic imaging verified changes in cranial temperature across the three conditions, actual brain temperature measurements were not obtained,” Gallup said.