No one knows why yawning is contagious, but there are new clues as to how it happens.PunchstockDo you feel a yawn coming on just looking at this picture? Yawning is known to be contagious — but the rule doesn't apply to autistic children. This finding could shed light on the social impairments of people with autism.
Atsushi Senju of Birkbeck College in London and his colleagues wanted to test the theory that contagious yawning is affected in people with autism. This kind of yawning is thought to be based at least partly on the capacity for empathy, which is compromised in autistic persons.
The researchers showed video clips of people either yawning or simply opening and closing their mouths to 49 children who were 7 years or older, half of whom were autistic.
The yawning faces triggered more than twice as many yawns in non-autistic children than in their autistic counterparts, they report in Biology Letters1. When shown the faces that were not yawning, however, both groups yawned about the same very infrequent amount, so the difference was not because non-autistic children simply yawn more in general.
The study was done with children in part because they are less likely to consciously suppress a yawn than adults; but the researchers expect that autistic adults would also be less susceptible to contagious yawning.
"This adds another piece to the autism puzzle — that there are deficits in some sorts of social communication," says Steven Platek, an evolutionary psychologist at the University of Liverpool, UK, who has studied contagious yawning. The study confirms Platek's previous finding that contagious yawning uses similar brain networks as does empathy2.
Mirror, mirror
No one knows exactly why yawning is contagious, although many theories have been posited — including the idea that yawning cools the brain and increases alertness, helping entire groups to become vigilant if one individual yawns.
Regardless of why it happens, there is also the question of how one person picks up a yawn from another. Some researchers have speculated that mirror neurons — brain cells that are activated not only when the person in question performs a particular movement, like waving their arms for example, but also when they see that movement being done by someone else — could be involved. Mirror neurons are thought to be the reason that humans can imitate others so successfully, and are thought to go wrong in autism.
"It's possible that contagious yawning has something to do with imitation," agrees Senju. But, he cautions, yawns are 'caught' rather than consciously imitated, and so might not be governed by a system that deals more with voluntary actions.
Watch me
Another possibility is that autistic children don't catch yawns as easily because they focus on a different part of others' faces. Normally, people spend most time looking at the eyes, but autistic people focus on the mouth. Although it might seem counterintuitive, the most potent stimulus for contagious yawning actually comes from a person's half-closing eyes rather than their gaping mouth, Platek says. So perhaps, says Platek, autistic children "don't pick up the right cues because they're reading the wrong part of the story".
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Even among the normal population, it's likely that people react differently to seeing someone near them yawn. "Within normal adults, there can be huge individual variability related to contagious yawning," Senju says. There's likely to be a continuum, with autistic people — and possibly others with similar social deficits — lying at the extreme end.
Senju and his team next plan to find out more about the development of contagious yawning in children, and to uncover the basis for the phenomenon under conditions of normal development. This should help to reveal how brain mechanisms differ in patients with conditions such as autism.
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