Authors: Christian Steyn¹; Tania Hanekom¹
¹Bioengineering, Department of Electrical, Electronic and Computer Engineering, University of Pretoria
Background: Cochlear implants (CIs) function by injecting current into the cochlea to stimulate the auditory nerve. However, this current can spread to adjacent structures, potentially causing unintended co-stimulation of the vestibular system or the facial nerve. This study utilizes a computational model to investigate the underlying mechanisms of vestibular co-stimulation in CI users.
Method: A person-specific, 3D finite element model (FEM) of the inner ear was developed to simulate electric potential distribution. The model features a detailed anatomical representation of the vestibular system. To assess the probability of neural excitation, the researchers calculated the second spatial derivative of the potential distribution, which is proportional to **Rattay’s activating function**, across the cochleo-vestibular volume.
Results: Preliminary simulations indicate that intracochlear stimulation significantly affects structures outside the cochlea. “Hotspots” of high activation probability were identified near all five vestibular organs: the saccule, utricle, and the three semicircular canal ampullae. The model predicts that monopolar stimulation results in a wider distribution of these extracochlear hotspots, while bipolar (apical reference) stimulation effectively limits spread beyond the cochlea.
Conclusion: These findings suggest that all vestibular organs are susceptible to unintended stimulation by CIs. The results are consistent with observed patterns of spread to other structures like the facial nerve. The study highlights that electrode stimulation strategy (e.g., bipolar vs. monopolar) plays a critical role in managing current spread and minimizing balance-related side effects in CI recipients.
