When you see someone else scratching an itch, do you start to feel itchy too? It turns out this phenomenon happens to many people and is a response known as “social contagion.” Some behavior is oddly contagious. When we see people yawn, we often find that we yawn in response. As it turns out, scratching is also contagious. It’s so contagious, that you might feel a little itchy just reading this.
“Sometimes even mentioning itching will make someone scratch,” Dr. Zhou-Feng Chen, of Washington University’s Center for the Study of Itch, claims. “Many people thought it was all in the mind, but our experiments show it is a hardwired behavior and is not a form of empathy.”
The topic is discussed in a report that was recently published in the journal Science. Research was conducted on mice. While mice were engaged in contagious scratching, the scientists studied the animals’ brain activity. The mice were literally shown a video of another mouse scratching an itch. In a matter of seconds, the test subjects began scratching.
“This was very surprising because mice are known for their poor vision,” Chen said, according to Medical News Today. “They use smell and touch to explore areas, so we didn’t know whether a mouse would notice a video. Not only did it see the video, it could tell that the mouse in the video was scratching.”
Apparently, when the mice watched the video of the itchy mouse, an area of the brain known as the suprachiasmatic nucleus (SCN), which regulates the sleep-wake cycle, exhibited increased activity. The SCN of the mice who caught the itch also released gastrin-releasing peptide (GRP). GRP is a substance that is involved in transmitting itch signals from the brain to the spinal cord. To verify the findings, the researchers then blocked the receptor in the brain that GRP binds to and then the mice no longer scratched themselves when they saw the other mouse scratch.
“The mouse doesn’t see another mouse scratching and then think it might need to scratch, too,” Chen explained of the behavior. “Instead, its brain begins sending out itch signals using GRP as a messenger.”
“It’s an innate behavior and an instinct. We’ve been able to show that a single chemical and a single receptor are all that’s necessary to mediate this particular behavior,” Chen explained. “The next time you scratch or yawn in response to someone else doing it, remember it’s really not a choice nor a psychological response; it’s hardwired into your brain.”
The same was determined to be true about yawning a few years ago, according to Science Daily.
“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,” Elizabeth Cirulli, author of an earlier study about contagious yawning, explained in 2014. Cirulli said that studying contagious yawning could provide insight into disorders like autism or schizophrenia, because people diagnosed with either seem to be less likely to engage in contagious yawning.
“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 at the time.
That earlier research also found that there was not a strong connection between contagious yawning and empathy, just as empathic emotions don’t appear to be the cause of a contagious itching.
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