From the WUSTL Newsroom…
Some behaviors — yawning and scratching, for example — are socially contagious, meaning if one person does it, others are likely to follow suit. Now, researchers at Washington University School of Medicine in St. Louis have found that socially contagious itching is hardwired in the brain.
Studying mice, the scientists have identified what occurs in the brain when a mouse feels itchy after seeing another mouse scratch. The discovery may help scientists understand the neural circuits that control socially contagious behaviors.
The study is published March 10 in the journal Science.
“Itching is highly contagious,” said principal investigator Zhou-Feng Chen, director of the Washington University Center for the Study of Itch. “Sometimes even mentioning itching will make someone scratch. 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.”
For this study, Chen’s team put a mouse in an enclosure with a computer screen. The researchers then played a video that showed 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.”
Next, the researchers identified a structure called the suprachiasmatic nucleus (SCN), a brain region that controls when animals fall asleep or wake up. The SCN was highly active after the mouse watched the video of the scratching mouse.
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