A Biophysical Model for Simultaneous Cochlear and Vestibular Nerve Stimulation: Insights into Neural Activation and...

Simultaneous hearing and balance restoration through combined cochlear-vestibular implants (CVIs) offers a promising treatment for patients with dual sensory deficits. However, the effects of electrical stimulation on neighboring neural structures in the inner ear remain poorly understood.

In this study, we present a detailed computational model of the human inner ear that simulates electrical stimulation of cochlear and vestibular nerves under clinically relevant conditions. The model integrates high-resolution micro-CT-based geometry, anisotropic tissue conductivities, and myelinated fiber models to predict neural activation patterns across a wide range of clinically relevant stimulation parameters.

Simulation results suggest that vestibular stimulation at clinically relevant amplitudes can influence cochlear nerve activation thresholds, particularly in basal cochlear regions. Conversely, cochlear stimulation had a comparatively weaker effect on vestibular activation. Interleaved stimulation with short interstimulus intervals (smaller 100 $\mu$ s) resulted in increased excitability in the non-targeted nerve population, suggesting the potential for undesired cross-talk effects. Pulse waveform characteristics, including phase duration and symmetry, further modulated the degree of crosstalk observed.

This model allows for comprehensive evaluation of scenarios that cannot be tested in humans due to ethical, practical, or technical limitations. As a result, it provides a valuable tool for exploring new combined simulation scenarios and may aid the development of newly designed implants.