March 2017 Vanderbilt University
Over 320,000 individuals have received cochlear implants (CIs) to restore hearing to the hearing impaired. Commercially available CIs have 12, 16, or 22 independent electrodes (depending on the manufacturer of the CI) which cover the entire frequency spectrum of the cochlea from 20,000 Hertz (Hz) at the base of to 200Hz at the apex. After implantation, audiologists individually adjust stimulation levels of each electrode following which all electrodes are turned on such that the whole frequency spectrum of speech can be appreciated. This is known as "standard of care" (SOC) programming. While postoperative speech understanding is significantly better than preoperative levels, even the best performers complain that the fidelity of natural hearing is not reproduced. Additionally, a significant minority achieves poor outcomes despite normally functioning equipment for reasons that are unknown but likely relate to poor neural survival; however, this cannot be confirmed as post-mortem histopathology is required to accurately document spiral ganglion cell count.
In recent years much attention has focused on the interface between the cochlear implant electrodes and the auditory neurons they are stimulating. Technological improvements at Vanderbilt in imaging processing have made it possible to determine the location of each electrode array in relationship to the frequency spectrum of the cochlea. Using this information, the investigators have developed a new method of CI programming which they call image-guided cochlear implant programming, or IGCIP in which sub-optimally placed electrodes are turned-off or deactivated. Sub-optimally placed electrodes are those where neighbouring electrodes are in closer proximity to the site of their neural stimulation. By deactivating such electrodes, channel interaction is reduced allowing a cleaner signal to be presented to the auditory nerve.
The investigators have implemented this strategy on 133 CIs of post-lingually deafened adult CI users with median use of SOC programming of 1.3 years. When trialling IGCIP, mean word scores increased from 48.8 to 53.3 correct, and mean sentence scores increased from 62.2 to 65.0 correct. Both of these finding were statistically significant.
Perhaps the most important metric is which map patients select for long term use - SOC or IGCIP. Ninety-six of the 133 (72.1%) participants elected to keep IGCIP for long term use despite prior research that shows that there is a bias for CI recipients to favour their original map over a new map. And, for the 28% for elected to keep their SOC map, the process involves no risk - the deactivated electrodes are simply reactivated. Given these exciting prospective findings, the investigators are now proposing a randomised controlled trial (RCT) for newly activated adult CI recipients with both the CI user and testing audiologist blinded as to program (SOC or IGCIP). The investigators hypothesise that CI recipients randomised to IGCIP will have improved hearing performance as assessed by both word and sentence testing.