Via EurekAlert: "Humans are born with 30,000 cochlear and vestibular hair cells per ear. (By contrast, one retina harbors about 120 million photoreceptors.) When a significant number of these cells are lost or damaged, hearing loss occurs. The major reason for hearing loss and certain balance disorders is that - unlike other species such as birds - humans and other mammals are unable to spontaneously regenerate these hearing cells. ... After years of lab work, researchers [have] found a way to develop mouse cells that look and act just like the animal's inner-ear hair cells - the linchpin to our sense of hearing and balance - in a petri dish. If they can further perfect the recipe to generate hair cells in the millions, it could lead to significant scientific and clinical advances along the path to curing deafness in the future. ... While researchers will ultimately need human hair cells, the mouse version is a good model for the initial phases of experimentation, he said. In addition to using mouse embryonic stem cells, the researchers used fibroblasts that had been reprogrammed to behave like stem cells: These are known as induced pluripotent stem cells, or iPS cells."