Yawning is infectious. When someone else yawns, you might yawn too, even if you're not tired. Now Italian researchers Elisabetta Palagi and Ivan Norscia believe they've solved the mystery of yawn contagion. 　　They say it's a form of emotional transmission - and that the closer you are genetically or empathically with the person yawning, the more likely it will be that you'll do the same. 　　Elisabetta Palagi, Pisa University Technician and fellow author of the paper on yawn contagion, said, "Through the face animals can be connected to each other socially and emotionally. 　　In fact there are evidence that emotional contagion pass through facial expression......Yawning is a good candidate to understand such emotional transmission between two different subjects." 　　Through studying more than 100 adults for more than a year, watching their subjects in a variety of settings, they found that empathy plays a part in controlling contagious yawning. The yawn response, the time gap between yawn trigger, is quicker and shorter between friends and kins. 　　Norscia believes the activation of the ventromedial prefrontal cortex in the brain is associated with the urge to yawn by contagion, especially when in response to yawning by friends or relatives. 　　Researchers believe the phenomenon could become useful in assessing people suffering from empathy deficit disorders, such as autism which hinders normal human interaction.