Why does hair pulling hurt? Blame your myelinated nociceptors

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Hairy situation

Yes, when someone pulls your hair – if you have enough hair that someone can pull it – it hurts. But the truth of why that is, and some of the how much and some of the how, has only recently become evident, thanks to a team of researchers scattered across several countries. Reader Sarah MacIntyre brought their work to Feedback’s attention.

The researchers are – there’s no better way to say this – painstaking in how they describe their discovery: “Single-unit axonal recordings revealed that a class of cooling-responsive myelinated nociceptors in human skin is selectively tuned to painful hair-pull stimuli.”

They took pains, also, to explain their work in a more human (rather than just technical) manner: “Together, we have demonstrated that hair-pulling evokes a distinct type of pain with conserved behavioral, neural, and molecular features across humans and mice.” And yes, we share this hair-pulling pain-specificity with our distant murine relatives.

Only humans, though, got examined verbally, as well as hair-pullingly. The scientists pulled hairs on the test subjects’ “forearm, hand, and foot regions”, then asked each hairy-armed, hairy-handed or hairy-footed person to indicate, via a questionnaire, whether the sensation was “throbbing”, “shooting”, “stabbing”, “hot-burning”, “aching”, “tender” or whatever. Some test subjects also had some head hairs pulled.

Hurts are not all equal. The study says that the amount of force required to produce a particular level of pain “was many times lower for hair pull compared to pinprick stimulation”.

Honestly?

If you want to know the truth about dishonesty, good luck to you. That seems the underlying message from František Bartoš at the University of Amsterdam.

His study called “The untrustworthy evidence in dishonesty research” looks at lots of evidence. Then it heaves what appears to be a sigh: “In conclusion, caution is advised when relying on or applying the existing literature on dishonesty.”

Recent years have seen a stream of academic papers about how often people lie or cheat and under what kinds of circumstances.

Some of those papers go further, offering certain tricks that can induce people to behave more honestly. One dishonesty-research project asked people to – just before doing a task on which they might feel tempted to cheat – write down the biblical Ten Commandments.

Bartoš tore into the statistics described in 99 published dishonesty-research papers – papers that other researchers have identified as being worth an extra, gimlet-eyed look.

He reports that many of those papers include numbers that are suspiciously low or high, or “contain results that are ‘too-good-to-be-true’”.

Bartoš does note that his own research, of course, could be wrong. And he writes that “there is reasonable hope” that the general situation is improving. Why? Because, recently, more people have been scrutinising the studies they read, rather than just assuming that everything is done both carefully and honestly.

Self-crumbling satellite

Almost no one wants to have a satellite fall from its decayed orbit, plummet down, down, down and bonk them. That’s why a team of researchers has been playing with ways to make a self-crumbling satellite – building it partially of material that will automatically degrade as the thing plunges into the atmosphere, rendering the big solid object into little bits that burn to near-nothingness.

In glorious techno-lingo, the scientists call their approach “the use of thermites to aid spacecraft demise during re-entry”. They reported their progress at a conference in Orlando, Florida, under the heading “Thermite-for-demise (T4D): From material selection to test campaign”.

Some juicy detail: “The charges are expected to ignite spontaneously during the re-entry phase, supplying additional heat to components critical for the on-ground casualty risk.”

Progress in any engineering adventure tends to come in clumps, each with a new little or big puzzle begging to be solved. Most recently, the team managed to “explain the reasons of the unexpected pressure build-up observed during the tests involving a fraction of activated thermite”.

If reliable, the basic satellite-self-destruction-and-scattering technique will give a new, more widely dispersed metaphorical meaning to Henry Wadsworth Longfellow’s poetic words, “I shot an arrow into the air / It fell to earth, I knew not where”.

Dangerous coconuts

Two further additions to Feedback’s collection of research studies with titles that are useful either for starting or stopping conversations.

First up, “Injuries due to falling coconuts” dropped into an issue of The Journal of Trauma in 1984. And then “Colonoscopy in the sitting position: Lessons learned from self-colonoscopy by using a small-caliber, variable-stiffness colonoscope” was inserted into the journal Gastrointestinal Endoscopy in 2006.

If you find an equally striking example, please send it (with citation details) to feedback@newscientist.com.

Marc Abrahams created the Ig Nobel Prize ceremony and co-founded the magazine Annals of Improbable Research. Earlier, he worked on unusual ways to use computers. His website is improbable.com.

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