Yawning, according to U.S. researchers, is the man as air-conditioning system. Experts at Princeton University found that people are much more susceptible to it in the cold and almost yawn at a time when the air temperature exceeds body temperature. From this they concluded that yawning need for thermoregulation of the brain. "It (the seasonal mismatch) proves the hypothesis that the mechanisms that control the urge to yawn, are involved in physiological thermoregulation, - said one of the study's authors, Andrew Gallup. - According to this theory, yawning causes fever of the brain and its physiological consequences are its cooling. The cooling effect of yawning, we believe, is the result of blood flow to the brain caused by the opening of the jaw, as well as countercurrent heat exchange with the environment due to a deep inhalation. " According to Gallup, in hot weather, yawning is reduced to nothing, because the ambient temperature is increased physiological effect of it is useless: glotnuv hot air, we do not provide the desired flow of the brain cool. At the same time, scientists believe, certain calendar periods can be for people with something like "thermal windows" when the number of spontaneous yawns peak. To test their hypothesis by Andrew Gallup and his colleague, Omar Eldakar conducted studies on 160 volunteers recruited from the Tucson (Arizona). Half of the subjects they observed during the winter at temperatures around 20 ° C, while the other half - in the summer, when air temperature is consistent with or slightly higher than the natural body temperature (36,6 ° C). To start the process of yawning, the participants of the experiment showed pictures of people yawning. "Our research shows that a higher frequency of yawning observed at that season when the ambient temperature was lower, even taking into account the statistical error, determined by factors such as humidity, time spent outdoors and duration of sleep at night - and boasted to Gallup. - Almost half the people in the course of the winter session began to yawn, while those in the summer had accumulated less than a quarter. In addition, the analysis of data for each season separately, we found that yawning is directly related to the amount of time people spent on the street. " The researchers said their work was the first scientific evidence that the frequency of yawning varies with the seasons. This discovery, scientists say, will come closer to understanding the brain and its diseases affecting. In addition, excessive yawning can now be regarded as a diagnostic tool to identify disorders of thermoregulation. A few years ago contributed to the study of yawning have a British psychologist at the University of Leeds. Having established a correlation between the level of sociability and students by how contagious yawning effect on them, they concluded that yawning - the most important social indicator that allows a great deal about the nature and state of mind of man. And before that, American psychologists from the University at Albany proved experimentally that, traditionally considered a sign of weariness yawning actually opens up a person a second wind, because the increased pressure and pulse rate, resulting in more blood rushes to your head and activates the heat transfer.