Our knowledge has enabled us to put a man on the moon, and yet we have not the slightest idea when it comes to yawning, something we probably do every night.
A research group from the Princeton University recently proposed that
yawning causes the walls of the maxillary sinus to expand and contract like a bellows, pumping air onto the brain, which lowers its temperature. Located in our cheekbones, the maxillary are the largest of four pairs of sinus cavities in the human head.
Gallup tested the idea in animals by implanting probes into rats' brain and recorded the brain-temperature changes. He found out that brain temperature increases in the run-up of a yawn, then starts to decline, before falling rapidly to pre-yawn temperature.
The study also helps to explain why humans have sinuses, whose existence has baffled scientists. This is like a unified study of sinus, yawning, and brain cooling, which is very interesting. Still, more tests are needed before we can confirm that yawning cools our brain--two subjects to prove something so poorly understood is statistically unacceptable.