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Itching Is Contagious Like Yawning! Blame the Brain!

Seeing someone scratch makes you feel itchy because it is a contagious social behaviour to which the brain is hardwired! The new findings are documented in a paper published in the journal Science.

When you see someone scratch himself, do you suddenly feel itchy too? Itching is actually a highly socially contagious behaviour, just like yawning is, according to a new study conducted by a team of researchers from the Washington University School of Medicine, St. Louis. The phenomenon is due to the brain being hardwired to respond in this manner, and not a result of empathy, explains lead author of the study, Zhou-Feng Chen. He also says that sometimes, just mentioning itching will prompt someone to scratch himself. So, next time you experience or see this behaviour, do not put the blame on yourself or the person, but blame the brain!

Chen and his colleagues came to this conclusion after observing a group of mice. They found that lab mice would feel itchy after seeing another mouse (in a video) scratch itself—an effect generated within seconds. This is surprising because mice normally have poor vision, and they use other senses, like smell and touch, to take in information from their environments—and, so a mouse noticing a detail from a video, and responding to it, is deemed unexpected.

When the researchers aimed at finding out the inner workings behind the behaviour, they spotted high activity in an area of the mice’s brain, known as the suprachiasmatic nucleus (SCN), after exposure to the video. The SCN, a structure controlling the timing of sleep and wakefulness in animals, would release a chemical called gastrin-releasing peptide, GRP, when the mice saw others scratching. According to Chen, GRP serves as an important ‘messenger’-transmitter of itch signals, relaying the information between skin and spinal cord. The team interpret these findings as evidence that the mice do not think before reacting with scratching themselves—they do not say to themselves that they need to scratch after seeing another mouse scratch. Rather, the scratching just happens because the brain sends out itch signals through the GRP.

Furthermore, as a way to confirm these theories, Chen and his team blocked GRP or its receptors, and found that these mice would not scratch upon seeing others scratch, while they would, otherwise, scratch if exposed to itch-causing substances. Chen, therefore, concluded that the contagious itching was not something the mice could control; according to him, it was innate, and an instinct.

So, scratching or yawning after seeing someone else doing so is not based on choice, and its cause is also not psychological. But, it is hardwired in the brain.

The team believes that their results will pave the way to a better understanding of neural circuits involved in socially contagious behaviours like scratching and yawning.

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