Influence of the Electrode-Neuron Interface and Asymmetry of Pulses on the Spread of Excitation in Cochlear Implants: A Computational Study.

Current spread in cochlear implants (CIs) degrades spectral resolution and speech perception by broadening neural excitation. Asymmetric pulses have been proposed to mitigate this issue; however, their practical application in CI strategies remains challenging owing to the potential temporal overlap between pulses from adjacent channels. In the present study, we employed a computational model to evaluate the effects of charge-balanced asymmetric pulses with varying second-phase durations on the spread of neural excitation (SOE) and neural activation. The SOE was assessed under different electrode-auditory nerve fiber (ANF) distances to explore the interaction between the pulse configuration and the neural interface. At greater electrode-ANF distances, increasing the second phase lowers the stimulation thresholds effect. However, at shorter distances, a prolonged second-phase duration induces neural inhibition and degraded neural activity patterns. Therefore, the efficacy of asymmetric pulses in reducing the SOE depends on the electrode position. Furthermore, a moderate increase in the second-phase duration may offer a promising direction for optimizing CI stimulation and enhancing speech perception.