Yawning might be more than a sign you are tired, it could also cool your brain.
A new study published in Physiology and Behavior links yawning to thermoregulation.
Humans have a tendency to yawn when tired, after waking up, or when we’re bored or under-stimulated. Of course, many of us yawn after seeing or hearing someone else yawn.
Some animals yawn to show dominance or to send a warning signal when threatened. Snakes yawn after eating a big meal to realign their jaws.
While some theorize that yawning is a natural reflex that increases the flow of oxygen to the brain, past scientific research has failed to find an association between the two.
Variations in brain temperatures have been associated with sleep cycles, cortical arousal – which increases wakefulness, vigilance, muscle tone and heart rate – as well as stress. According to the study’s authors, we yawn to maintain a balanced brain temperature, keeping it at a steady level.
The researchers anticipated that yawning would decrease in cooler temperatures since the brain temperature would be lower in colder weather.
To find out if they were right, the researchers conducted two tests. In one, team members from the University of Vienna measured how often pedestrians engaged in contagious yawning during winter and summer months. In the second test, conducted earlier in the US state of Arizona where the climate is generally warm and dry, pedestrians there were asked to look at pictures of people yawning to see if it would make them yawn.
The Vienna tests revealed that people there yawned more in summer than in winter, while the opposite was true for those tested in Arizona. People there yawned more in winter than in summer.
An analysis of the test results found that neither the seasons, nor the amount of daylight hours experienced by those tested in Austria and Arizona, had an impact on their yawning behavior.
Instead they found that people in both locations tended to yawn contagiously most frequently when the temperature was about 20 degrees Celsius.
This contagious yawning was reduced when temperatures rose to about 37 degrees C during the summer of Arizona or during the freezing temperatures of the Austrian winter.
According to the study’s lead author, Jorg Massen from the University of Vienna, yawning to cool the brain doesn’t work when the air temperature is cooler than normal body temperature, and may also not be necessary or even can be harmful, when the temperature is freezing cold.
The researchers found that cooling the brain works to improve a person’s arousal and mental efficiency. So with this in mind, they also suggested that individuals spreading yawning behavior through contagious yawning could be doing so in order to improve overall vigilance within a group.
The research team involved with this study was made up of scientists from the University of Vienna, Austria, Nova Southeastern University in Florida and the State University of New York in Oneonta, New York.