This is why yawns are contagious

The reasons we reciprocate yawns is hard-wired into our brains, a primitive reflex that if better understood could help treat disorders such as Tourette syndrome.

Researchers at the University of Nottingham in England say yawning is triggered involuntarily when others yawn because of a human trait called echophenomena.

Ecophenomena drives us to imitate other people's words and actions, researchers explained in a study published Thursday in Current Biology. But it's also found in neurodevelopment conditions such as Tourettes, autism and epilepsy, for which the researchers are trying to find alternative treatments. 

The team took 36 people, showed them videos of people yawning and then counted the yawns each participant reciprocated and those yawns they fought against. They found the ability to suppress a yawn after someone else does it is "limited" and becomes more difficult if someone tells a person not to do it. In addition, the study found applying electrical stimulation drove the necessity to yawn, which could lead to medical advances. 

"Using electrical stimulation we were able to increase excitability and in doing so increase the propensity for contagious yawning," said Georgina Jackson, a professor in cognitive psychotherapy at Nottingham. "In Tourettes, if we could reduce the excitability we might reduce the ticks."

Researchers could "potentially reverse" these disorders if there was a better understanding of how excitability is connected to them, said Stephen Jackson, a professor of cognitive neuroscience at Nottingham who led the study.

The finding aside, the researchers said this phenomenon is not unique to humans. Chimpanzees and dogs also find yawns contagious.

In fact, the reasons we yawn when we're tired remains vexing to researchers because many theories lack evidence. For instance, he said it's been floated that we yawn because we lack oxygen or need to cool the brain, "but the evidence is lacking and weak," said Stephen Jackson. 

Even the cause of contagious yawning has had its own theories.

"The popular theory for contagious yawning is that it is linked with empathy for others, mimicry and social bonding," Stephen Jackson said. "But again the evidence for this is weak. I still think that much more research is required to understand the function and biology of yawning."

Follow Sean Rossman on Twitter: @SeanRossman