Yawning prevents sleep by sending cooled blood to the brain, according to researchers at Princeton, the University of Maryland School of Dentistry and the State University of New York. Cooling the brain causes it to work more efficiently, blocking sleep.Continue Reading
Although yawning is common in humans and higher animals, it still isn't fully understood. Hypotheses that it is due to fatigue or oxygen deprivation have not held up to testing, but Andrew Gallup's 2007 hypothesis that yawning promotes alertness by cooling the brain is faring better. Gallup has been testing his hypothesis at Princeton University by recording brain and body temperature changes in rats and humans before, during and after yawning. His work shows that temperature spikes before a yawn and drops afterward, suggesting that yawns are triggered by an increase in brain temperature and work to lower that temperature.
Gary Hack of the University of Maryland School of Dentistry suggests that the mechanism behind this change is that yawning acts to expand and contract the maxillary sinus, pumping cool air to lower the brain's temperature. In separate work, the SUNY researchers found that breathing through the nose or holding a cold pack to the forehead eliminate yawning triggered by social cues. This supported the brain cooling hypothesis and led the SUNY researchers to believe that yawning in response to yawns by others may have evolved as a means of maintaining group alertness.Learn more about Human Anatomy