This is so cool!

In a study that appeared in March in the Journal of Clinical Investigation, the researchers used viruses to implant genes for light sensitivity into mouse embryos of a deaf lineage. The genes went to work in the auditory pathways of the mouse brains, creating light-sensitive patches on the membranes of their spiral ganglion neurons and other neurons. The scientists then directed LED light onto these neurons and recorded brain stem activity—an essential integration step in auditory processing.

The activity indicated the deaf mice successfully perceived the light as sound. Compared with stimulation from traditional cochlear implant electrodes, the light produced more precise neural activity in the brain stem, similar to normal hearing. The mice also exhibited a high level of sound discrimination that current prosthetics cannot achieve.