The idea that yawning is contagious is nothing new, however researchers from Duke University are now finding out more about the phenomenon as they observed that contagious yawning decreases with age.

The researchers recorded the number of times 328 healthy individuals yawned while watching a three-minute video. The number of yawns per person ranged from zero to 15, with some participants more susceptible to contagious yawns. A total of 222 participants contagiously yawned at least one time. "Contagious yawns" are defined as when someone is "thinking, seeing or hearing about yawning." Spontaneous yawning is believed to be due to boredom or feeling tired. While spontaneous yawning begins while still in the womb, contagious yawning doesn't start until early childhood.

Researchers found the only independent factor linked to contagious yawning was age, as older participants were less likely to yawn as often. Previous studies suggested a connection between yawning and variables such as empathy, feelings of tiredness and energy level.

"The lack of association in our study between contagious yawning and empathy suggests that contagious yawning is not simply a product of one's capacity for empathy," study author Elizabeth Cirulli, an assistant professor of medicine at the Center for Human Genome Variation at Duke University School of Medicine, said in a university news release.

A better grasp of contagious yawning could subsequently result in a deeper understanding of general human biology as well as of certain disorders such as autism or schizophrenia, as these conditions are associated with decreased susceptibility with the phenomenon.

"It is possible that if we find a genetic variant that makes people less likely to have contagious yawns, we might see that variant or variants of the same gene also associated with schizophrenia or autism," Cirulli said. "Even if no association with a disease is found, a better understanding of the biology behind contagious yawning can inform us about the pathways involved in these conditions."

The study was published in the March 14 issue of the journal PLOS ONE.