Researchers at Binghamton University have just zeroed in on the reasons why we yawn just before and after sleeping.
"Brains are like computers," Andrew Gallup, a researcher in the Department of Biology at Binghamton University who led the study, told Discovery News.
"They operate most efficiently when cool, and physical adaptations have evolved to allow maximum cooling of the brain," he added.
To reach the conclusion, the expert along with colleagues Michael Miller and Anne Clark analyzed 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.
Gallup said that contagious yawning is thought to be an evolved mechanism for keeping groups alert so they "remain vigilant against danger."
For the study, the scientists exposed parakeets to three different conditions: increasing temperature, high temperature and a moderate control temperature.
While the frequency of yawns did not increase during the latter two conditions, it more than doubled when the researchers increased the bird's ambient temperature.
The study has been published in the journal Animal Behavior.
"Based on the brain cooling hypothesis, we suggest that there should be a thermal window in which yawning should occur," Gallup said.
"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 expert said.
The parakeets yawned as predicted.
It's now believed yawning operates like a radiator for birds and mammals.