Never mind that stifling a yawn is the polite thing to do. The next time you feel the urge, open wide. Yawning drives away drowsiness by activating certain muscles to increase heart rate. It also appears to have a cooling effect on the brain, which heightens attentiveness, according to a recent study at the State University of New York-Albany. Researchers found that yawning decreased when volunteers held cool packs to their foreheads. "When you yawn, you take an unusually large volume of air into the lungs, which sends a wave of cool blood to the brain," explains study coauthor Gordon Gallup. He hypothesizes that mental processing slows down when the brain's temperature rises above normal. In fact, paratroopers and skydivers often find themselves yawning before they jump, perhaps to enhance their brain function.
Is yawning contagious? Actually, yes. Nearly half the study participants yawned while watching videotapes of others doing so. Gallup says yawns may spread by triggering an empathy reflex that keeps a group alert and on the lookout for predators. So yawn away. Or opt for the polite alternative: Breathing deeply through the nose has the same brain-cooling effect.