Stem cells have been used to restore hearing in animals for the first time, a huge step toward treating deafness in humans, British researchers say. Scientists at the University of Sheffield said hearing partially improved in gerbils when nerves in the ear which pass sounds into the brain were rebuilt using stem cells, the BBC reported Wednesday. Achieving the same amount of improvement in people could lift hearing levels from being unable to hear traffic to hearing a conversation, they said, although they caution treating humans with stem cells remains a distant prospect. In some people, profound hearing loss occurs when nerve cells that should pick up electrical signal produced in the ear are damaged. The goal of the University of Sheffield researcher was to replace those nerve cells, called spiral ganglion neurons, in gerbils with new ones created with stem cells. The researchers detected the improvement in the animals\' hearing by measuring brainwaves. On average, 45 percent of their hearing range was restored by the end of the study, researchers said.