Where technology meets anatomy

A DOCTOR WRITES: CALUM GEARY is about to make medical history by becoming the first child in the Republic to undergo highly …

A DOCTOR WRITES:CALUM GEARY is about to make medical history by becoming the first child in the Republic to undergo highly specialised ear surgery. Later this month, surgeons at Manchester University Hospital will place an auditory brainstem implant (ABI) in the deaf child's brain.

Calum was born without a fully functioning cochlea in his inner ear. He has no hearing (auditory) nerves, so sounds cannot travel between either inner ear and the part of the brain that processes this signal and turns it into intelligible words or sounds.

Sound travels from the outer ear, through the tympanic membrane into the middle ear, from where it reaches the cochlea in the inner ear. The cochlea then sends signals through the auditory nerve that runs from the inner ear to the base of the brain – an area known as the brain stem.

The auditory nerve is the eighth in a series of 12 cranial nerves, each of which has a specialist function. There are two of each cranial nerve, one on either side of the head.


Auditory brainstem implants consist of electrodes placed in the part of the brain (the cochlear nucleus) located in the brainstem. In addition, a tiny microphone is positioned by the ear to pick up sounds and a decoding chip is placed under the skin to transmit information picked up by the microphone.

An auditory brainstem implant does not restore normal hearing, but it helps most people distinguish sounds such as telephone rings and car horns. Some people get good word recognition, while others get more general sound cues.

A key element in a successful outcome is the provision of intensive specialist speech therapy post-operatively.

As soon as the ABI is switched on – usually about four to eight weeks after surgery – the recipient must begin to learn the meaning of the different sounds he will hear. Some children who have received an ABI have shown improvements in cognitive development.