Scratching an itch may be an everyday activity, but it’s also a longstanding conundrum to scientists who have never been sure if the urge originated in the skin or the brain. Until now. A new study from University of Minnesota neuroscientists appears to show that both the itch, and the relief scratching provides, come from specialized cells in the spinal cord, the New York Times reports.
“It’s as if there’s a little brain in there that creates this state in which scratching—which normally excites pain cells—instead inhibits them,” says a study co-author. The researchers injected monkeys with histamines, and immediately saw their spinothalamic neurons begin firing. When they scratched the itchy skin, that activity stopped. “It’s the first time I’ve ever seen a noxious stimulus—the scratching—stop the firing of cells.”