Investigations of cochlear implant stimulation using a finite element head model

Abstract

The cochlear implant (CI) is a medical technology that is widely used to treat hearing loss. In this, current pulses are injected at the electrode pads on the implanted intracochlear electrode array to stimulate the neurons in the modiolus. All the current must travel to the return electrode, which is located remotely on the side of the head for monopolar (MP) stimulation. Our understanding of the current conduction pathways and voltage distribution resulting from CI stimulation can help improve future designs and implementation strategies. A computational model would serve as a useful tool to improve our understanding of the current conduction pathways and voltage distributions as a result of MP stimulation. However, most of these models are only interested in the local cochlea region and assume particular boundary conditions. For a more reliable result, a Human Electro-Anatomical Total Head Reconstruction (HEATHER) was developed. This finite element (FE) model was created from the female Visible Human Project dataset to include twelve tissues and geometries of the cochlear implant and electrode array. A simulation of MP stimulation using HEATHER showed that current exits the cochlea via the modiolus, the basal end of the cochlea and the cochlear walls, and travels to the implant via the cranial cavity or scalp. All return locations were similar except for the internal auditory meatus. Blocking the basal end of the cochlea increased current going to the modiolus and cochlear walls. Global voltage distributions were sensitive to tissue resistivities of large tissues (scalp, bone, grey matter). Local voltages are also dependent on boundary conditions. With HEATHER, studies that would otherwise have been difficult or not feasible to perform in vivo can be tested in silico, making it valuable for CI research. Its flexibility allows it to be also used in other fields. The workflow used to generate HEATHER can be applied to other anatomical models.