Why does injury or surgery in some people lead to lasting pain, while in others the wound heals and the pain resolves along with it? A new study takes on that question by comparing rats that develop chronic pain after nerve injury with identically injured animals that do not. Researchers directed by Frank Porreca and Theodore Price at the University of Arizona, Tucson, found that differences in pain modulation by the central nervous system underlie the rats’ opposite fates. The data suggest that descending inhibitory mechanisms protect some rats by continuously blocking pain. The study, led by first authors Milena De Felice, Raul Sanoja, and Ruizhong Wang, was published online July 9 in Pain.