The relation between polarity sensitivity and neural degeneration in a computational model of cochlear implant stimulation.

The main aim of this computational modelling study was to test the validity of the hypothesis that sensitivity to the polarity of cochlear implant stimulation can be interpreted as a measure of neural health. For this purpose, the effects of stimulus polarity on neural excitation patterns were investigated in a volume conduction model of the implanted human cochlea, which was coupled with a deterministic active nerve fibre model based on characteristics of human auditory neurons. The nerve fibres were modelled in three stages of neural degeneration: intact, with shortened peripheral terminal nodes and with complete loss of the peripheral processes.

Place pitch versus electrode location in a realistic computational model of the implanted human cochlea.

Place pitch was investigated in a computational model of the implanted human cochlea containing nerve fibres with realistic trajectories that take the variable distance between the organ of Corti and spiral ganglion into account. The model was further updated from previous studies by including fluid compartments in the modiolus and updating the electrical conductivity values of (temporal) bone and the modiolus, based on clinical data. Four different cochlear geometries are used, modelled with both lateral and perimodiolar implants, and their neural excitation patterns were examined for nerve fibres modelled with and without peripheral processes.

The impact of internodal segmentation in biophysical nerve fiber models.

Implementation of double cable models to simulate the behavior of myelinated peripheral nerve fibers requires defining a segmentation of the internode between successive nodes of Ranvier. The number of internodal segments is a model parameter that is not well agreed on, with values in the literature ranging from 1 to more than 500. Moreover, a lot of studies also lack a sensitivity study or a rationale behind the implementation used.

Neural excitation patterns induced by phased-array stimulation in the implanted human cochlea.

Conclusions: Phased-array stimulation is a promising technique, which uses electrical interaction to focus the stimulation in cochlear implants, at the expense of limited threshold shifts. It has potential advantages over, for example, tripolar stimulation.

Objectives: Current spread imposes limitations in cochlear implants.