Deaf since birth, three-year-old Grayson Clamp was born missing his cochlear nerves. Recently, however, Grayson became the first child from the U.S. to receive an experimental auditory brain stem implant. This video shows his reaction upon hearing his dad's voice for the first time.

The cochlear nerves are the bundles of axons responsible for carrying auditory signals from his inner ear to his brain. Grayson's implantation procedure was originally developed for adults with auditory nerve tumors, but researchers think it could be especially effective in children, whose brain plasticity could afford them enormous potential to interpret sound, organize it, and use it to make sense of the world.

When you're finished weeping the happiest tears of your life, you can read more about the procedure at UNC Health Care and CBS News.