(CN) – A new study published in the journal Science offers evidence that itching, yawning and other behaviors are socially contagious.
“Sometimes even mentioning itching will make someone scratch,” lead author Zhou-Feng Chen said.
Chen’s team from the Washington University School of Medicine placed a mouse in an enclosure with a computer screen, which played a video of another mouse scratching.
“Within a few seconds, the mouse in the enclosure would start scratching too,” Chen said. “This was very surprising because mice are known for their poor vision. 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.”
The team found that a structure called the suprachiasmatic nucleus – a region of the brain that controls when animals fall asleep or wake up – was highly active after the mouse watched the video of the scratching mouse.
“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,” Chen said.
Seeing other mice scratch prompted the experimental mouse to release a chemical substance called gastrin-releasing peptide, or GRP. In 2007, Chen’s team identified GRP as a key transmitter of itch signals between the spinal cord and the skin.
“The mouse doesn’t see another mouse scratching and then think it might need to scratch too,” Chen said. “Instead, its brain begins sending out itch signals using GRP as a messenger.”
Chen’s team also used other methods to block GRP, or the receptor it binds to on neurons, which stopped the contagious behavior. The mouse was still able to scratch when exposed to itch-inducing substances.
“It’s an innate behavior and an instinct,” Chen said. “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.”