Brown BJ et al. A Neural Basis for Contagious Yawning. Current Biology, August 2017.

Why do we yawn if someone else does? Ecophenomena drives us to imitate other people's actions, but it's also found at excessive levels in neurodevelopment disorders such as Tourette’s, autism, and epilepsy, for which scientists have been intensely trying to find treatments. A new study suggests that the human propensity for contagious yawning is triggered involuntarily by primitive reflexes in the primary motor cortex, an area of the brain responsible for motor function. In the study, 36 adults who viewed video clips showing someone else yawning were asked to resist the act. Results showed that 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. This study demonstrates that the “urge” is intensified by trying to stop yourself. Moreover, increasing brain excitability in test subjects using electrical stimulation was found to increase the propensity for contagious yawning. This experiment suggests that reduced excitability in Tourette’s might reduce the tics (repetitive involuntary movements) and vocalizations in affected individuals. Scientists are still puzzled by the reasons why we yawn when we're tired. For example, one theory suggests that we yawn when we lack oxygen or need to cool our brains. Another theory for the cause of contagious yawning is that it is linked with empathy for others, mimicry, and social bonding. But the evidence for these theories remains very weak, and more research is needed to understand the function and biology of yawning.

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