John Brigande of Oregon Health and Science University has developed an experimental gene therapy that generates hair cells that are damaged or missing in deaf animals.

His team injected mice embryos with a gene called Atoh1, apparently a hair- cell master switch that activates genes that turn developing cells into hair cells. The cells grew hair cells in precisely the right location in their cochleas, and the cells made connections to nerve fibers that travel to the brain, converting movements into electrical nerve pulses.

The work could speed the development of a treatment for hearing loss.