Scientists have spotted a small set of easily overlooked brain cells that is activated during persistent pain — the kind that lasts long after an initial injury. The research was performed in mice, but if it can be confirmed in humans, the work could lead to new therapies for chronic pain. Such pain affects roughly one in five people worldwide. “Pain is in your head. But it is very real,” says Nicholas Betley, a biologist at the University of Pennsylvania in Philadelphia and a co-author of a new study describing the findings. The authors’ experiments also show that the release of a specific signalling chemical in the brain can dampen the activity of the persistent-pain neurons, suggesting that the brain itself has an innate pain-killing mechanism.