The science of itching

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Nation Wong/Corbis

Nation Wong/Corbis

Scientists have found a way to manipulate the neurons in mice that respond to itch — and, in the process, have settled a longstanding debate: Is itchiness just a form of pain, or a separate, unique sensation?

It turns out the brain treats itch and pain completely differently, even though they can both be excruciating. Researchers from Washington University in St. Louis, MO, and from Peking University in Beijing learned this by giving a neurotoxin to a group of mice; it knocked out cells with a certain neuronal receptor that’s known to respond to itch. Afterward, the mice could no longer respond to any itchy stimuli. They didn’t flinch. They made no effort to scratch. But they did respond to pain just like other mice do. That finding, released today by Science, strongly suggests that two separate neural pathways process pain and itch.

So why would animals, and humans, have a unique itch response? Pain helps us to avert danger, clearly. If something hurts we avoid it. But an itchy feeling tell us… to give ourselves a quick rub? It seems strange. A startling and fascinating piece in the New Yorker last year explains what little we know about this common sensation and how it’s perceived by both body and mind. (That piece also includes one of the most harrowing clinical tales I’ve ever heard. It makes for excellent reading.) Today’s research news offers a little more clarity in the science of itching — but only a little.