How to Scratch an Itch Without Actually Scratching It

January 27, 2014 | Andy Cush

The human brain, for all its power, is a fallible thing. Look no further than /r/illusionporn, or the myriad optical tricks floating around elsewhere on the internet for proof. Now, German researchers have come up with a new practical application for the mind’s endless capacity for fooling itself: scratching itches without actually scratching them.

Christoph Helmchen and his team at the University of Lübeck set out to whether it was possible to lessen an itching sensation solely by giving the brain a visual cue that it was being scratched. First, they injected subjects in one arm with histamine, a chemical that induces itching; then, they gave subjects a red mark identical to the one produced by the chemical on their opposite arm, so that both arms looked the same. New Scientist explains what happened next:

…They placed a large vertical mirror in front of the itchy arm, blocking off the subject’s view of their right arm and reflecting back the non-itchy one in its place . They asked the volunteers to look only at the reflected limb in the mirror, whilst a member of the team again scratched each arm. This time the participants felt relief when the unaffected, reflected arm was scratched.

Admittedly, the researchers’ methodology was a bit more complicated than most would want to try at home, and the subjects’ satisfaction was markedly lower than those who actually had their itch scratched, but still: That’s the wrong arm. You are so dumb, brain!

(Photo: Donnie Ray Jones)