Brain hardwired to respond to others' itching

March 9, 2017, Washington University School of Medicine
Itching is a highly contagious behavior. When we see someone scratch, we're likely to scratch, too. New research from the Washington University Center for the Study of Itch shows contagious itching is hardwired in the brain. Credit: Michael Worful

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, PhD, 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."

When researchers showed a mouse a video of another mouse scratching, the live mouse began scratching, too. Credit: Washington University Center for the Study of Itch

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.

When the mouse saw other mice scratching—in the and when placed near scratching littermates—the brain's SCN would release a chemical substance called GRP (gastrin-releasing peptide). In 2007, Chen's team identified GRP as a key transmitter of itch signals between the skin and the spinal cord.

"The mouse doesn't see another 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 various methods to block GRP or the receptor it binds to on neurons. Mice whose GRP or GRP receptor were blocked in the brains' SCN region did not scratch when they saw others scratch. But they maintained the ability to scratch normally when exposed to itch-inducing substances.

Chen believes the contagious itch behavior the engaged in is something the animals can't control.

"It's an innate behavior and an instinct," he said. "We've been able to show that a single chemical and a single receptor are all that's necessary to mediate this particular behavior. 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 .

Explore further: Neuroscience: Why scratching makes you itch more

More information: "Mice, Not Just Primates, Feel the Impulse of Contagious Itching," Science(2017). DOI: 10.1126/science.aak9748

Related Stories

Neuroscience: Why scratching makes you itch more

October 30, 2014
Turns out your mom was right: Scratching an itch only makes it worse. New research from scientists at Washington University School of Medicine in St. Louis indicates that scratching causes the brain to release serotonin, ...

Scientists unravel mechanisms in chronic itching

October 15, 2013
Anyone who has suffered through sleepless nights due to uncontrollable itching knows that not all itching is the same. New research at Washington University School of Medicine in St. Louis explains why.

Potential new target identified for treating itch

July 19, 2016
Researchers have found how sensory nerve cells work together to transmit itch signals from the skin to the spinal cord, where neurons then carry those signals to the brain. Their discovery may help scientists find more effective ...

Itch neurons play a role in managing pain

February 22, 2017
There are neurons in your skin that are wired for one purpose and one purpose only: to sense itchy things. These neurons are separate from the ones that detect pain, and yet, chemical-induced itch is often accompanied by ...

Recommended for you

Research shows signalling mechanism in the brain shapes social aggression

October 19, 2018
Duke-NUS researchers have discovered that a growth factor protein, called brain-derived neurotrophic factor (BDNF), and its receptor, tropomyosin receptor kinase B (TrkB) affects social dominance in mice. The research has ...

Good spatial memory? You're likely to be good at identifying smells too

October 19, 2018
People who have better spatial memory are also better at identifying odors, according to a study published this week in Nature Communications. The study builds on a recent theory that the main reason that a sense of smell ...

How clutch molecules enable neuron migration

October 19, 2018
The brain can discriminate over 1 trillion odors. Once entering the nose, odor-related molecules activate olfactory neurons. Neuron signals first accumulate at the olfactory bulb before being passed on to activate the appropriate ...

Scientists discover the region of the brain that registers excitement over a preferred food option

October 19, 2018
At holiday buffets and potlucks, people make quick calculations about which dishes to try and how much to take of each. Johns Hopkins University neuroscientists have found a brain region that appears to be strongly connected ...

Gene plays critical role in noise-induced deafness

October 19, 2018
In experiments using mice, a team of UC San Francisco researchers has discovered a gene that plays an essential role in noise-induced deafness. Remarkably, by administering an experimental chemical—identified in a separate ...

Weight loss success linked with active self-control regions of the brain

October 18, 2018
New research suggests that higher-level brain functions have a major role in losing weight. In a study among 24 participants at a weight-loss clinic, those who achieved greatest success in terms of weight loss demonstrated ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

RobertKarlStonjek
not rated yet Mar 10, 2017
Scratching is just one of many behaviours that are contagious. The reason why should be fairly clear. When activities are clumped together it is much safer in a natural environment, behaviours such as being vigilant, that is, when one person or conspecific senses danger than all others who see that behaviour also act *as if* they also sensed the danger and so become hypervigilant. Sensing that it is OK to relax, laugh, scratch etc is just the other side of the same coin.

Animals doing things in concert like hunting or feeding or even sleeping is highly effective and so we can expect that some kind of predisposition to do so has evolved and become innate with laughing and emotional reactions being spandrels of the evolved predisposition.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.