Scientists probe the meanings of a yawn

Ho-hum. Although everyone yawns, not everyone finds it easy to “catch” a yawn.

Ho-hum. Although everyone yawns, not everyone finds it easy to “catch” a yawn.

Studies have shown that only 50 to 60 per cent of us will yawn when someone else yawns in our sight. Being susceptible to contagious yawning appears to be an outside window on the extent to which someone is empathetic and able to distinguish one’s own mental state from that of others.

A 2007 study found that psychology students were more susceptible to contagious yawning than a group of engineering students.

Everyone — and most higher species (vertebrates), from apes to lions to dogs — yawns. The average human is estimated to yawn 240,000 times in a lifetime, often starting when we’re still in the womb. But researchers have shown yawns are contagious only among chimpanzees and humans.

A study in the current issue of the journal Child Development reports that contagious yawning doesn’t occur in most children until they’re about 4 years old. The research involved adult volunteers yawning in front of kids age 1 to 6 identified as undergoing typical mental development.

But the researchers found that among 30 children aged six to 15 with autism spectral disorders, those with severe autism seemed to miss the cues of the social yawn. Youngsters diagnosed with milder variants of autism spectral disorders were more likely than the more severely affected patients to catch a yawn, but less so than those in a developmentally normal control group.

“This lends support to the idea that the social mind develops over time through a process of mimicry and feedback,” said Molly Helt, a doctoral student in psychology at the University of Connecticut. “If we can identify a lack of mimicry of facial expressions early, it could be a way to identify potential neurodevelopment disorders such as autism.”

The contagiousness of yawning appears to extend beyond sight. Canadian researchers did an experiment that combined brain imaging and the sounds of people yawning and making other sounds. They found that subjects experienced more activity in the brain’s right inferior frontal gyrus when they heard yawns as opposed to ordinary breathing, and told experimenters they felt more like yawning at that point. The brain structure is associated with emotional response to others and language processing.

Other researchers have noted the link to emotion and yawning recently, including work presented by a Dutch researcher at the International Conference on Yawning in June that suggests adult yawning is linked to erotic response to another person. Even though the conference was held in Paris, the theory may still be a tough sell to a significant other if you yawn during an intimate moment.

However, the physiology of yawning seems to offer a bit of cover on this point. Studies have shown that while we do yawn when we’re sleepy, the act is in reality connected more to maintaining or increasing alertness. And, by the way, biologists have noted yawning plays a role in the mating rituals of some species of birds and perhaps apes.

While it was once thought the yawn was a way to boost oxygen levels, that notion has been refuted by studies that found no difference in the amount of oxygen in the blood before and after yawning.

But stretching the jaw does boost circulation to the brain. Researchers at the University of Albany suggested in a 2007 paper that yawning helps cool the brain by increasing blood flow and drawing in cooler air with the deep breath, also increasing mental efficiency. And as anyone who’s had a yawnfest in a stuffy meeting room knows, yawning is more common in warm than cool settings.

Researchers also noted that multiple sclerosis — a disorder of the central nervous system that strips nerves of their insulating material — has a connection to dysfunction of the body’s temperature-regulating system. Excessive yawning is a common symptom of the illness and some patients report they have short-term relief from symptoms such as muscle weakness and mood alteration after they yawn.

Still other research, mostly in mice, suggests that yawning is a stress-coping mechanism as well as a vigilance enhancer. Even skater Apollo Ono, who has a habit of yawning just before he starts a race, has confided that while he thinks it boosts oxygen levels for him, it also “lets the nerves out.”