Biologists have provided further evidence of the hypothesis of yawning as a mechanism of cooling the brain: the students who have pressed to the carotid artery ice pack, when watching movies with yawning people yawned less than if the package was hot. However, the authors of an article published in the journal Physiology & Behavior, note that in their study there was no direct evidence of temperature change of the brain — it was measured on the skin in the orbital area, not inside the skull.
Many vertebrates yawn, and the length of the yawn mammals correlates with relative brain size and density of neurons. It is logical to assume that yawning has an adaptive function, but scientists still have not agreed what it is. According to one hypothesis, yawning is need to cool the brain — contraction of muscles increases blood circulation, and the heat is dissipated in the air stream. The hypothesis supported by some experimental results: to yawn want less if you actively breathe in through the nose, and the result is yawn the brain temperature is reduced. However, not all the scientific community agrees with causality — perhaps yawning is accompanied by a rise in temperature of the brain, but is not involved in thermoregulation.
Scientists from Italy and the United States under the leadership of Andrew Gallup (Gallup Andrew) from southeastern University Nova checked whether to reduce the level of contagious yawning indirect cooling of the brain. 92 students in five minutes was pressed to the neck opposite the carotid artery (it carries blood to the brain) heat packs: room temperature (22 degrees Celsius), hot (42 degrees) or cold (4 degrees). After five minutes the volunteers had delayed the package and immediately looked minute video with a yawning nine other people. While watching the video, the researchers recorded the number of blunders, and after him, the students filled out a questionnaire about whether they would like to yawn.
To ensure that the thermal bags pressed against the carotid artery, can change the temperature of the brain, was pre-tested on two volunteers. Within five minutes they kept at the neck packs with the same temperatures as in the main experiment, and at the beginning and end of the temperature of the skin over the inner corner of the eye (this area is used for non-invasive measurement of brain temperature) was measured using a radiometric thermal imaging camera with high resolution.
Package a temperature of 42 degrees Celsius for five minutes increased the brain temperature by 0.26 degrees, and the temperature of 4 degrees was reduced by the same amount. To yawn after watching the movie I wanted on average, 67 percent of volunteers, mostly when they were pressed hot pack (85 percent), and much lower if the brain is cooled (48%, p = 0.002). The frequency of yawning was also significantly higher in the first case (p = 0.001).