Why Is Your First Instinct After Hurting Your Finger to Put It in Your Mouth?

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If you close your fingers in a car door or slam your funny bone into a wall, you might find your first reaction is to suck on your fingers or rub your elbow. Not only is this an instinctive self-soothing behavior, it's a pretty effective technique for temporarily calming pain signals to the brain.

But how and why does it work? To understand, you need to know about the dominant theory of how pain is communicated in the body.

In the 17th century, French scientist and philosopher René Descartes proposed that there were specific pain receptors in the body that "rang a bell in the brain" when a stimulus interacted with the body, Lorne Mendell, a professor of neurobiology and behavior at Stony Brook University in New York, tells Mental Floss. However, no study has effectively been able to identify receptors anywhere in the body that only respond to painful stimuli.

"You can activate certain nerve fibers that can lead to pain, but under other circumstances, they don't," Mendell says. In other words, the same nerve fibers that carry pain signals also carry other sensations.

In 1965, two researchers at MIT, Patrick Wall and Ronald Melzack, proposed what they called the gate control theory of pain, which, for the most part, holds up to this day. Mendell, whose research focuses on the neurobiology of pain and who worked with both men on their pain studies, explains that their research showed that feeling pain is more about a balance of stimuli on the different types of nerve fibers.

"The idea was that certain fibers that increased the input were ones that opened the gate, and the ones that reduced the input closed the gate," Mendell says. "So you have this idea of a gate control sitting across the entrance of the spinal cord, and that could either be open and produce pain, or the gate could be shut and reduce pain."

The gate control theory was fleshed out in 1996 when neurophysiologist Edward Perl discovered that cells contain nociceptors, which are neurons that signal the presence of tissue-damaging stimuli or the existence of tissue damage.

Of the two main types of nerve fibers—large and small—the large fibers carry non-nociceptive information (no pain), while small fibers transmit nociceptive information (pain).

Mendell explains that in studies where electric stimulation is applied to nerves, as the current is raised, the first fibers to be stimulated are the largest ones. As the intensity of the stimulus increases, smaller and smaller fibers get recruited in. "When you do this in a patient at low intensity, the patient will recognize the stimulus, but it will not be painful," he says. "But when you increase the intensity of the stimulus, eventually you reach threshold where suddenly the patient will say, 'This is painful.'"

Thus, "the idea was that shutting the gate was something that the large fibers produced, and opening the gate was something that the small fibers produced."

Now back to your pain. When you suck on a jammed finger or rub a banged shin, you're stimulating the large fibers with "counter irritation," Mendell says. The effect is "a decrease in the message, or the magnitude of the barrage of signals being driven across the incoming fiber activation. You basically shut the gate. That is what reduces pain."

This concept has created "a big industry" around treating pain with mild electrical stimulation, Mendell says, with the goal of stimulating those large fibers in the hopes they will shut the gate on the pain signals from the small fibers.

While counter irritation may not help dull the pain of serious injury, it may come in handy the next time you experience a bad bruise or a stubbed toe.

Alcohol-Producing Gut Bacteria May Harm Livers—Even if You Don't Drink

itakdalee/iStock via Getty Images
itakdalee/iStock via Getty Images

Teetotalers might think their liver is safe from the damaging effects of alcohol consumption, but new research is hinting that even non-drinkers and light drinkers might have cause for concern. It turns out a type of gut bacteria is capable of producing alcohol—and enough of it to potentially cause some pretty serious health consequences, including liver disease.

A study led by Jing Yuan at the Capital Institute of Pediatrics in Beijing, China and published in the journal Cell Metabolism offers details. After evaluating a patient with auto-brewery syndrome (ABS), a rare condition brought on by consumption and fermentation of sugary foods that leaves a person with high blood alcohol levels, researchers made an intriguing discovery. Rather than finding fermenting yeast that may have led to the condition, the patient’s stool contained Klebsiella pneumonia, a common gut bacteria capable of producing alcohol. In this subject, K. pneumonia was producing significantly more alcohol than in healthy patients.

The patient also had nonalcoholic fatty liver disease (NAFLD), characterized by fatty deposits in the liver. While many cases of NAFLD are relatively benign, too much fat can become toxic. Examining 43 other subjects with NAFLD, scientists found that that K. pneumonia was both present and potent, pumping out more alcohol than normal in 60 percent of participants with NAFLD. In the control group, a surplus was found in only 6.25 percent.

To further observe a correlation, scientists fed the bacteria to healthy, germ-free mice, who began to see an increase in fat in their livers after only one month. While not conclusive proof that the bacteria prompts NAFLD, it will likely trigger additional research in humans.

It’s not yet known how K. pneumonia acts in concert with the bacterial profile of the gut or what might make someone carrying stronger strains of the bacteria. Luckily, K. pneumonia can be treated with antibiotics. That’s good news for people who might never touch a drink and still find themselves with a damaged liver.

[h/t Live Science]

5 Hilarious Discoveries from the 2019 Ig Nobel Prize Winners

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andriano_cz/iStock via Getty Images

Each September, the Ig Nobel Prizes (a play on the word ignoble) are given out to scientists who have wowed the world with their eccentric, imaginative achievements. Though the experiments are usually scientifically sound and the results are sometimes truly illuminating, that doesn’t make them any less hilarious. From postal workers’ scrotal temperatures to cube-shaped poop, here are our top five takeaways from this year’s award-winning studies.

1. Left and right scrota often differ in temperature, whether you’re naked or not.

Roger Mieusset and Bourras Bengoudifa were awarded the anatomy prize for testing the scrotum temperatures in clothed and naked men in various positions. They found that in some postal workers, bus drivers, and other clothed civilians, the left scrotum is warmer than the right, while in some naked civilians, the opposite is true. They suggest that this discrepancy may contribute to asymmetry in the shape and size of male external genitalia.

2. 5-year-old children produce about half a liter of saliva per day.

Shigeru Watanabe and his team nabbed the chemistry prize for tracking the eating and sleeping habits of 15 boys and 15 girls to discover that, regardless of gender, they each produce about 500 milliliters of spit per day. Children have lower salivary flow rates than adults, and they also sleep longer (we produce virtually no saliva when we sleep), so it seems like they may generate much less saliva than adults. However, since children also spend more time eating than adults (when the most saliva is produced), the average daily levels are about even—at least, according to one of Watanabe’s previous studies on adult saliva.

3. Scratching an ankle itch feels even better than scratching other itches.

Ghada A. bin Saif, A.D.P. Papoiu, and their colleagues used cowhage (a plant known to make people itchy) to induce itches on the forearms, ankles, and backs of 18 participants, whom they then asked to rate both the intensity of the itch and the pleasure derived from scratching it. Subjects felt ankle and back itches more intensely than those on their forearms, and they also rated ankle and back scratches higher on the pleasure scale. While pleasure levels dropped off for back and forearm itches as they were scratched, the same wasn’t true for ankle itches—participants still rated pleasurability higher even while the itchy feeling subsided. Perhaps because there’s no peace quite like that of scratching a good itch, the scientists won the Ig Nobel peace prize for their work.

4. Elastic intestines help wombats create their famous cubed poop.

In the final 8 percent of a wombat’s intestine, feces transform from a liquid-like state into a series of small, solid cubes. Patricia Yang, David Hu, and their team inflated the intestines of two dead wombats with long balloons to discover that this formation is caused by the elastic quality of the intestinal wall, which stretches at certain angles to form cubes. For solving the mystery, Yang and Hu took home the physics award for the second time—they also won in 2015 for testing the theory that all mammals can empty their bladders in about 21 seconds.

5. Romanian money grows bacteria better than other money.

Habip Gedik and father-and-son pair Timothy and Andreas Voss earned the economics prize by growing drug-resistant bacteria on the euro, U.S. dollar, Canadian dollar, Croatian luna, Romanian leu, Moroccan dirham, and Indian rupee. The Romanian leu was the only one to yield all three types of bacteria tested—Staphylococcus aureus, Escherichia coli, and Vancomycin-resistant Enterococci. The Croatian luna produced none, and the other banknotes each produced one. The results suggest that the Romanian leu was most susceptible to bacteria growth because it was the only banknote in the experiment made from polymers rather than textile-based fibers.

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