Why Do We Scratch an Itch?

The science of itching is fascinating and strange. In 2008, Atul Gawande wrote what may be the definitive work of popular science journalism on the issue. In "The Itch," he wrote about the neuroscience of itching and its many causes—including remarkable cases in which some circuitry had clearly gone wrong, driving people mad with the need to scratch (the piece includes one unforgettable account of a woman who involuntarily scratched through her own skull and into brain tissue).

But the question is, which neural circuitry was going haywire, causing the pathological itching? Today, researchers report in the journal Science (abstract) that they may have found an answer. Using mice genetically modified to have light-sensitive neurons—a fascinating area of biotechnology known as optogentics—they shined lights into the animals' brains. The light switched off a circuit in an area called the parabrachial nucleus, a part of the brain stem, and stopped the mice from scratching after being presented with a itchy stimulus. Sweet relief—and hope, perhaps, for chronic scratchers everywhere.