3From One Electrode to Open-Set Speech: A History of the ABI

F1979: one electrode, one patient

The ABI was born at the House Ear Clinic in Los Angeles. In 1979 William House and William Hitselberger implanted a single ball-type electrode on the surface of the cochlear nucleus of a woman who had just had her second vestibular schwannoma removed and would otherwise have been left completely deaf. The electrode produced useful auditory sensations, proving for the first time that hearing could be evoked by stimulating the brainstem itself rather than the ear.

The idea did not come from nowhere. Earlier work had shown that electrical stimulation of the human cochlear nucleus could produce sound percepts, and neurosurgeons already recorded evoked potentials from the region during operations. House and Hitselberger turned this observation into a therapy for the most hopeless of deaf patients, those whose nerves had been sacrificed to remove their tumours.[2008][2019]

FFrom single channel to multichannel

A single electrode could signal that sound was present but conveyed almost no detail. Through the 1980s and 1990s, in collaboration with the Huntington Medical Research Institute and then the Cochlear Corporation, the device evolved into multi-electrode arrays on a mesh backing, two- and three-contact prototypes giving way to eight-electrode and finally twenty-one-electrode arrays driven by modified cochlear implant processors.

More electrodes meant more pitch percepts and the chance to switch off contacts that caused side effects, but they did not transform the device into a cochlear implant. Because a flat array cannot map cleanly onto the brainstem’s frequency layout, the gains were real but bounded. Still, by the late 1990s the multichannel ABI was a credible clinical device rather than an experiment.[2008][2002]

C2000: FDA approval for NF2

In 2000 the multichannel Nucleus ABI received approval from the United States Food and Drug Administration for use in NF2 patients aged twelve and older. Notably, the approval set no audiologic criteria; candidacy turned on the diagnosis, age, motivation and realistic expectations, because the device was offered to patients who were being rendered deaf by tumour surgery rather than selected by hearing thresholds.

A European multicentre investigation of the same multichannel system, reported around the same time, confirmed the picture that had emerged from Los Angeles. The great majority of NF2 recipients gained auditory sensations and better recognition of the stress and rhythm of speech, which substantially aided lip-reading, but only a small minority understood words or sentences by sound alone. The ABI had become the standard of care for hearing in NF2 while remaining, for most, a sound-awareness device.[2002][2020]

CThe European turn: non-tumour adults and children

The most important shift came from Europe. From the late 1990s Vittorio Colletti in Verona and others began offering the ABI to patients who had never had a tumour, those with cochlear nerve aplasia, ossified cochleae, head-trauma nerve avulsion, severe malformations, or failed cochlear implants, often through a retrosigmoid approach. Strikingly, these non-tumour adults did far better than NF2 patients, with many achieving open-set speech understanding, suggesting that the cochlear nucleus damage in NF2, not the device, was the main limit on performance.

Colletti and Sennaroglu then extended the device to young deaf children with absent cochlear nerves or inner ear malformations, implanting them early to exploit the plasticity of the developing auditory brain. International consensus meetings, including one in Ankara, set out criteria for paediatric and non-NF2 implantation, and inner ear malformation classifications helped define exactly which children were beyond a cochlear implant.

The arc of the ABI is therefore a widening one: from a single electrode meant only to give an NF2 patient awareness of sound, to a multichannel device that can, in selected non-tumour adults and children, restore genuinely useful, sometimes open-set, hearing. Its history is a reminder that the same hardware can mean very different things depending on why the pathway failed.[2005][2024]