Yawning does not occur because you are tired, bored or even need oxygen. Instead yawning helps to regulate the brain’s temperature by cooling it. That is the theory proposed by Gary Hack, DDS of the University of Maryland School of Dentistry and Andrew Gallup, PhD of Princeton University. “The brain is exquisitely sensitive to temperature changes and therefore must be protected from overheating,” the authors write in the journal Medical Hypotheses. “Brains, like computers, operate best when they are cool.” How does yawning cool the brain? Hack and Gallup think the walls of the human maxillary sinus flex during yawning like a bellows, which in turn facilitates brain cooling.