ECAP growth function to increasing pulse amplitude or pulse duration demonstrates large inter-animal variability that is reflected in auditory cortex of the guinea pig.

Victor Adenis,Elisabeth Mamelle,Boris Gourévitch,Dan Gnansia,Matthieu Recugnat,Jean-Marc Edeline,Yann Nguyen,Pierre Stahl,Manuel S Malmierca

doi:10.1371/journal.pone.0201771

Abstract

Despite remarkable advances made to ameliorate how cochlear implants process the acoustic environment, many improvements can still be made. One of most fundamental questions concerns a strategy to simulate an increase in sound intensity. Psychoacoustic studies indicated that acting on either the current, or the duration of the stimulating pulses leads to perception of changes in how loud the sound is. The present study compared the growth function of electrically evoked Compound Action Potentials (eCAP) of the 8th nerve using these two strategies to increase electrical charges (and potentially to increase the sound intensity). Both with chronically (experiment 1) or acutely (experiment 2) implanted guinea pigs, only a few differences were observed between the mean eCAP amplitude growth functions obtained with the two strategies. However, both in chronic and acute experiments, many animals showed larger increases of eCAP amplitude with current increase, whereas some animals showed larger of eCAP amplitude with duration increase, and other animals show no difference between either approaches. This indicates that the parameters allowing the largest increase in eCAP amplitude considerably differ between subjects. In addition, there was a significant correlation between the strength of neuronal firing rate in auditory cortex and the effect of these two strategies on the eCAP amplitude. This suggests that pre-selecting only one strategy for recruiting auditory nerve fibers in a given subject might not be appropriate for all human subjects.

Highlights

Over the past decades, cochlear implants have become the most successful neuroprosthesis and are largely used for restoring hearing
Variability of ECAP growth functions to increasing pulse amplitude or pulse duration shows the N1-P2 amplitude as a function of the charges for the 2 stimulation strategies: in this particular case, there was no difference in the growth function obtained with the PA and PD strategy
As the N1 wave could not be systematically quantified because of its proximity with the stimulation artifact, the P2-N2 wave was used in the subsequent analyses to quantify the evoked Compound Action Potentials (eCAP) amplitude

Summary

Introduction

Cochlear implants have become the most successful neuroprosthesis and are largely used for restoring hearing. They are far from perfectly mimicking the processing that takes place in a normally functioning organ of Corti. The ANRT (a governmental agency) did not have additional role in designing the study, data collection and analysis, decision to publish or preparation of the manuscript. Oticon Medical provided support in the form of the salaries of authors PS and DG and some of the research material (electrode arrays, stimulation board), but did not have additional role in designing the study, data collection and analysis, decision to publish or preparation of the manuscript. The specific roles of PS and DG are articulated in the “author contributions” section

Methods

Results

Discussion

Conclusion