Why Do We Yawn?
For years it was thought that yawning increased oxygen intake by expelling excess carbon dioxide. But strong evidence put the kibosh on this theory back in the 1980s. New research suggests that yawning might help cool the brain. Our brains use about 15 percent of the calories we burn (a lot considering the brain is only 3 percent of our body weight). When the brain heats up from burning all that fuel, our ability to process information suffers. Like the internal fan of a computer, yawning may help keep our brains humming along at an optimal temperature.
Gordon G. Gallup Jr., Ph.D., a professor of psychology at the State University of New York at Albany, tested this theory by looking at yawn rates in subjects who held cool compresses to their foreheads or breathed through their noses, both of which are thought to cool the brain. These folks yawned less than others. It seems a chilled-out brain reduces the need to yawn.
Gallup also has a notion about those notoriously contagious yawns circling around story time and conference tables (you might even be yawning right now): "We think yawning evolved to promote mental efficiency." So, he speculates, contagious yawning encourages the vigilance of the pack. One yawning individual sends a powerful signal to the group (revving up my brain over here!). Others take the subconscious cue and begin yawning too to increase their own alertness.
Explain It to Your Kids
Have your child run or jump in place for 2 minutes. Explain that his brain gets hot from burning energy, just like all this activity warms his body. Eventually his brain would get slow and tired, just like he would if he continued to run and jump. Then turn on a fan and have your child feel the cooling breeze. A yawn might be our head's way of fanning itself on the inside. The deep intake of breath sends a blast of fresh air across blood vessels in our head, cooling the blood that's on its way to the brain. Yawning may help blow away the extra heat, allowing our brains to get cooking again.