Yawning cools the brain Tuesday, 16 December 2008 Jennifer Viegas Discovery News
The new findings also explain why we yawn when we're tired (Source: iStockphoto) Related Stories Oxygen may ease headache and migraine, Science Online, 25 Jul 2008 Empathy makes you 'catch' a yawn, Science Online, 15 Aug 2007 Yawn & Oxygen If your head is overheated, there's a good chance you'll yawn, according to a new study that found the primary purpose of yawning is to control brain temperature. The finding solves several mysteries about yawning, such as why it's most commonly done just before and after sleeping, why certain diseases lead to excessive yawning, and why breathing through the nose and cooling off the forehead often stop yawning. The key yawn instigator appears to be brain temperature. "Brains are like computers," says Andrew Gallup, a researcher in the Department of Biology at Binghamton University who led the study, which has been accepted for publication in the journal Animal Behavior. "They operate most efficiently when cool, and physical adaptations have evolved to allow maximum cooling of the brain." He and colleagues Michael Miller and Associate Professor Anne Clark analysed yawning in parakeets as representative vertebrates because the birds have relatively large brains, live wild in Australia, which is subject to frequent temperature swings, and, most importantly, do not engage in contagious yawning, as humans and some other animals do. Contagious yawning is thought to be an evolved mechanism for keeping groups alert so they "remain vigilant against danger," says Gallup. Thermal window For the bird study, the scientists exposed parakeets to three different conditions: increasing temperature, high temperature and a control temperature. While yawning did not increase during the latter two conditions, it more than doubled when the researchers increased the bird's ambient temperature. "Based on the brain cooling hypothesis, we suggest that there should be a thermal window in which yawning should occur," says Gallup. "For instance, yawning should not occur when ambient temperatures exceed body temperature, as taking a deep inhalation of warm air would be counterproductive. "In addition, yawning when it is extremely cold may be maladaptive, as this may send unusually cold air to the brain, which may produce a thermal shock." The parakeets yawned as predicted. It's now believed yawning operates like a radiator for birds and mammals. If air in the atmosphere is cooler than brain and body temperatures, taking it in quickly cools facial blood that, in turn, cools the brain and may even alter blood flow. Prior studies reveal yawning leads to a heightened state of arousal, so a morning yawn may function somewhat like a cup of coffee in providing a jolt of energy. The new findings also explain why tired individuals often yawn, since both exhaustion and sleep deprivation have been shown to increase deep brain temperatures, again prompting a yawn-driven cool down. Yawning additionally appears to facilitate transitional states of the brain, such as going from sleep to waking periods. Seizure signal Professor Gordon Gallup Jr, a psychologist at the State University of New York, Albany, did not work on the study, but, as Andrew Gallup's father, paid close attention to the research. He is also a leading expert on the science of yawning and other widespread evolved traits. "It is interesting to note that instances of excessive yawning in humans may be indicative of brain cooling problems," says Gallup Jr, pointing out that patients with multiple sclerosis often experience bouts of excessive yawning "and MS involves thermoregulatory dysfunction." He says, "Bouts of excessive yawning often precede the onset of seizures in epileptic patients, and predict the onset of headaches in people who suffer from migraines." In the future, researchers may focus more on brain temperature and its role in diseases and their symptoms. But the new study on yawning changes the popular notion that yawns are mere signs of boredom. On the contrary, as Gallup says, "yawning more accurately reflects a mechanism that maintains attention, and therefore should be looked at as a compliment!" Tags: anthropology-and-sociology, sleep, brain-and-nervous-system http://www.abc.net.au/science/articles/2008/12/16/2447520.htm
