Abstract
Cochlear implants use electrical stimulation of the auditory nerve to restore the sensation of hearing to deaf people. Unfortunately, the stimulation current spreads extensively within the cochlea, resulting in “blurring” of the signal, and hearing that is far from normal. Current spread can be indirectly measured using the implant electrodes for both stimulating and sensing, but this provides incomplete information near the stimulating electrode due to electrode-electrolyte interface effects. Here, we present a 3D-printed “unwrapped” physical cochlea model with integrated sensing wires. We integrate resistors into the walls of the model to simulate current spread through the cochlear bony wall, and “tune” these resistances by calibration with an in-vivo electrical measurement from a cochlear implant patient. We then use this model to compare electrical current spread under different stimulation modes including monopolar, bipolar and tripolar configurations. Importantly, a trade-off is observed between stimulation amplitude and current focusing among different stimulation modes. By combining different stimulation modes and changing intracochlear current sinking configurations in the model, we explore this trade-off between stimulation amplitude and focusing further. These results will inform clinical strategies for use in delivering speech signals to cochlear implant patients.
Highlights
COCHLEAR implants (CIs) are considered life-changing devices for the rehabilitation of severe-to-profound hearing loss [1] [2]
Complementary to previous modelling work on CIs [23]–[25], we propose a novel in-vitro model approach in this paper, by separating the stimulating and sensing/recording electrodes to obtain the full distribution of the spread-induced voltage (SIV)
With COMSOL simulation, we found that the selections of transverse resistances can be optimized to better fit in-vivo electrical field imaging (EFI) data (Fig. S8 and Table S2), with root-mean-square errors below 7%
Summary
COCHLEAR implants (CIs) are considered life-changing devices for the rehabilitation of severe-to-profound hearing loss [1] [2]. Despite CIs having up to 26 intracochlear electrodes that can be used for the stimulation [6], traditionally only between 4-8 independent channels of information have been reported [7], [8]. These issues can be largely attributed to current spread, that results in “blurring” of the input signal at the neuronal level [9]. The importance of current is seen not just in cochlear implants and in other neural prostheses that require independent spatial channels for optimal performance, rather than just time domain parameters such as stimulation rate [10], [11]
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