Contagious yawning is not the only form of echophenomena (automatic imitation, or "echoing", of words or actions) we know of, but it's by far the most common. And our urge to yawn is increased if we are instructed to resist yawning. But the scientists counted more stifled (yet still noticeable) yawns in this group, and the participants reported stronger urges to yawn than the group that was allowed to do so.
The researchers showed 36 adults video clips of people yawning, and then instructed them to alternate between trying to resist their own yawns, and yawning as much as they liked. As the researchers used TMS, it was also possible to increase the "excitability" in the motor cortex and thus even increase people's tendency to contagious yawns.
Scientists say that this happens for 60-70% of people. The fact that TMS readings of the motor cortex proved to be such accurate predictors of the behavior suggests that this area of the brain has a key role to play in the behavior, possibly in echophenomena at large. "Various studies have proposed links between contagious yawning and empathy, yet the research supporting this connection is mixed and inconsistent", psychologist at SUNY Polytechnic Institute, Dr Andrew Gallup, told BBC News.
Professor Stephen Jackson, who led the study, said the findings could be "particularly important" in helping scientists understand conditions such as epilepsy, dementia, autism, and Tourette syndrome.
They found that the human intensity for contagious yawning is triggered involuntarily by an area of the brain called primitive reflexes in the primary motor cortex.
Another holiday weekend, another price hike
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Echophenomena can also be seen in a wide range of clinical conditions linked to increased cortical excitability and/or decreased physiological inhibition such as epilespsy, dementia, autism and Tourette syndrome.
In one experiment, researchers asked the participants to try and stifle their yawns while viewing yawn videos or just yawn freely if they were unable to do so. "We are looking for potential non-drug, personalized treatments, using TMS that might be effective in modulating imbalances in the brain networks", Jackson said.
Based on these examinations, the researchers found that it's hard to resist yawning when you see someone yawn, and that urge only gets stronger when you're told not to yawn. And trying to stifle a yawn by keeping your mouth tightly shut will only make you want to do it more.
Regardless of the cause, it's probably a safe bet that you're yawning right now.