Yawning is typically linked to tiredness, but a group of researchers from Princeton and the University of Arizona have found it may simply be a means to regulate brain temperature.
Photo by Tambako the Jaguar.
The researchers found yawning frequency correlates with the season and yawning is more likely when the temperature outside is less than the temperature of the brain. Their argument is that keeping your mouth agape helps regulate the temperature of the brain by exposing the roof to cooler air. In the author's previous studies, cooler brains have been linked to alertness, which might help explain why we yawn when we're tired.
Yawning May Cool the Brain [Discovery News]