This Is Why You Can't Tickle Yourself

"It actually feels better when someone else is touching you."
hands touching

Each week, we read what's going on the world of science and bring the wildest findings straight to you. Here's the latest:

Why you can’t tickle yourself

It feels different when other people touch you, compared to when you touch yourself. This is obvious when you try to tickle yourself and it doesn’t make you laugh, or when it doesn’t feel as good to massage your own shoulders as when someone else does it.

“That is not just because you can relax better because you don’t have to do anything, it actually feels better when someone else is touching you,” says Rebecca Böhme, a neuroscientist at Linköping University in Sweden and the first author of a new study in Proceedings of the National Academy of Sciences (PNAS).


The research looked at people’s brains using fMRI when others were touching them on the arm, or when they were touching themselves on the arm. They found that when we touch ourselves, the brain dulls the experience. “We found that many areas reduced their activity during self-touch,” Böhme tells me.

Being touched by others activated more areas in the brain, like ones involved in the processing of tactile sensations, and also areas related to social cognition and reward, leading to a more intense sensation than with self-touch.

When another person makes physical contact with us, it’s a form of communication. It could be to get our attention, or to offer support, or show love. It’s important for us to be aware of those kinds of touch, Böhme says, and so the brain might be filtering out sensations that aren’t as important—like us touching ourselves, “which is most of the time only nervous fidgeting or self-grooming. Even though the actual sensation on our skin might be the exact same, your brain can differentiate which one is of importance because it comes from another person and which one is not because it comes from you.”

Though it would be nice to be able to give yourself a proper massage, this distinction between self and other touch is probably important. Studies have found that people with schizophrenia are more successful at tickling themselves, suggesting that they might not have the same brain de-activations during self-touch.


“This could be related to certain illusions they have: when they perceive sensations that actually come from themselves as alien,” Böhme tells me.

Are there super poopers among us?

If you’re unlucky enough to get Clostridium difficile, or C. diff, a bacterium that causes severe diarrhea, your doctor might recommend you get a fecal transplant. Yup, that means getting somebody else’s poop and putting it into your body. Well, sort of.

A fecal transplant is when the bacteria is isolated from the poop of a healthy person and given to another. The hope is that the healthy bacteria from the donor will restore the health of the other person’s microbiome, the community of bacteria living in their body. It’s thought to do so by re-introducing microbial diversity, or beneficial species that may have been lost. But new research suggests that all poop may not be created equal.

Last year, The Infectious Diseases Society of America officially added fecal transplant to its list of treatment recommendations for C. diff, but the allure of poop transplants reaches farther than that. Differences in the microbiome have been associated with many conditions, from irritable bowel syndrome (IBS) to obesity to diabetes, and even psychiatric conditions like anxiety or bipolar disorder. Could a fecal transplant help with those too?

In a new review in Frontiers in Cellular and Infection Microbiology, researchers wrote that so far, fecal transplants have been just an okay treatment option for those other chronic conditions—there’s been a lot of variability in how people respond. It seems like fecal transplant success is dependent on the unique qualities of the donor poop—“leading to the proposition of the existence of [fecal microbiota transplantation] super-donors,” the authors write.


“The existence of super-donors is still a hypothetical concept supported by only a couple of studies,” first author Brooke Wilson, a doctoral candidate at the University of Auckland, tells me. But from the limited work that’s out there, a super-donor might be a person whose poop would lead to more successful fecal transplants than others’ poop.

“We see transplants from super-donors achieve clinical remission rates of perhaps double the remaining average,” senior author Justin O'Sullivan said in a press release. “Our hope is that if we can discover how this happens, then we can improve the success of fecal transplantation and even trial it for new microbiome-associated conditions like Alzheimer's, multiple sclerosis, and asthma."

What makes someone a super pooper? They might have higher microbial diversity overall, but also have higher levels of a few very important species that are thought to be important for health. They could also have just the right balance of bacterial species, and interactions between those species, as well as other microorganisms, like viruses.

It’s probable that different medical conditions would have their own super poop associated with them, so there’s likely multiple types of super poop to discover. “Each person's stool is unique which poses the question, whose stool is best?” Wilson says. “Studying super-donors could be a logical step forward in trying to understand what it is about their stool that makes it effective at treating a particular disease.”


Liberal and conservative American states use weed differently

As more states legalize weed in some way, either medically or recreationally, researchers are watching to see how those policies might change marijuana use. A new study in the International Journal of Drug Policy found that there might be other influences in the amount of weed people use besides just marijuana laws, like the already existing policies of that state that have nothing to do with marijuana.

The research looked at how liberal a state’s laws were using something called a “policy liberalism index” which compares policies that liberal and conservative states usually differ on like gun control, abortion access, tax progressivity, collective bargaining, and more.

They found that teens and young adults who live in states with more liberal policies reported higher rates of marijuana use than those in states with conservative policies. But—the rates of cannabis use disorder were significantly lower in liberal compared to conservative states among people ages 12 to 17, and marginally lower for ages 26 and up. Cannabis use disorder is when a person can’t stop using weed even if they want to, has cravings for weed, and finds that their marijuana use is negatively interfering with their life.

The results show that policy around marijuana doesn’t exist in a vacuum, says Morgan Philbin, first author and social and behavioral scientist at Columbia University Mailman School of Public Health. “A medical cannabis law in Hawaii is enacted into a very different state-specific context than, say, in Arizona,” she says. “In particular, we had suspected that there might be some unobserved heterogeneity across states that this focus on just medical cannabis laws (versus the broader policy climate) is not fully capturing.”


Still, the research just found an association for now, meaning it doesn’t mean that being in a liberal state causes lower rates of cannabis use disorder. “Instead, it highlights how states may differ beyond the existence of medical cannabis policies, and that these differences merit attention," Philbin says.

Your weekly health and science reads

Trapped in a hoax: survivors of conspiracy theories speak out. By Ed Pilkington in The Guardian.
Five stories of people who got targeted by conspiracy theories, like being wrongly accused of being the Parkland shooter or leading a pedophile ring in a pizza restaurant.

Flu science points to another culprit when vaccines fail — us. By Helen Branswell in Stat.
If you get the flu this year, even after getting your shot, don’t immediately blame the shot. “Sometimes our immune systems simply don’t follow the instructions a vaccine tries to give them.”

No One Is Prepared for Hagfish Slime. By Ed Yong in The Atlantic.
“It expands by 10,000 times in a fraction of a second, it’s 100,000 times softer than Jell-O, and it fends off sharks and Priuses alike.”

How to Stop Rogue Gene-Editing of Human Embryos? By Pam Belluck in The New York Times.
It’s tricky to enforce a no-gene-editing-unconsenting-babies law.

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