Watch the exact moment a deaf toddler hears for the very first time

A 17-month old deaf toddler named Alex Frederick recently had an experimental device implanted directly into his brainstem — a device that has yet to be approved for children in the United States. This is the exact moment it started to work.

It's called an auditory brainstem implant (ABI) — a surgically implanted electronic device that provides a sense of sound to people who have a sensorineural hearing impairment. This type of profound deafness is typically caused by an illness or injury that resulted in damage to the cochlea or auditory nerve. In the case of Alex, he was born premature, which doctors say caused his deafness.

Normally, this condition can be treated with a cochlear implant — a tried-and-true technology that uses electrodes to stimulate auditory nerves. Doctors tried to give Alex a cochlear implant, but they had to bail from the surgery when it became clear that it wouldn't work due to the irregular structure of his inner ear.

Alex's dad, Phil Frederick, eventually discovered the work of Dr. Vittorio Colletti who has done pioneering work for ABI in Italy. The timing was right as the technology was about to undergo clinical trials in the U.S. to gain FDA approval.

ABI works similarly to a cochlear implant, but instead of stimulating the cochlea, electrode arrays send signals directly to the brainstem. It is, for all intents and purposes, a cybernetic device.

ABC News describes the rest:

After five and a half hours in the operating room, Alex was taken into intensive care. His head was wrapped in a cap of bandages, under which was a cluster of wire that doctors hoped would allow him to hear. He then went home to recover.

Several weeks after surgery, the big day arrived. Alex and his family returned to Massachusetts Eye and Ear Infirmary in November to have his ABI switched on for the first time. The wires connected the device inside his head to a sound generator controlled from a computer, where a doctor could manipulate the sound level on the device.

Alex's parents decided that they wanted the first sound their son to hear to be his sisters' voices, so after the device was turned on, the girls started talking, but Alex didn't elicit a reaction. Others in the room tried raising the sound level, but still nothing at first.

Then, to everyone's surprise, a doctor in the room slammed her keys into the side of a desk, and Alex turned towards the sound.

"All of the sudden he just looked," Stephanie said. "He stopped everything that he was doing and he looked." "I felt right away, 'oh he definitely heard that,'" Phil added. "I knew, he was completely focused on his toy and then he just— he looked."

From here, Alex will have to undergo speech therapy to learn to associate and distinguish incoming sounds.

Read more at ABC.