Exponential fitting of spread of excitation response measurements in cochlear implants

Tobias Rader; Pascal Nachtigäller; Theresa Linke; Tobias Weißgerber; Uwe Baumann

doi:10.1016/j.jneumeth.2023.109854

Exponential fitting of spread of excitation response measurements in cochlear implants

J Neurosci Methods. 2023 May 1:391:109854. doi: 10.1016/j.jneumeth.2023.109854. Epub 2023 Apr 7.

Authors

Tobias Rader¹, Pascal Nachtigäller², Theresa Linke³, Tobias Weißgerber⁴, Uwe Baumann⁴

Affiliations

¹ Division of Audiology, Department for Otorhinolaryngology, University Hospital, Ludwig-Maximilians-Universität München, Munich, Germany. Electronic address: tobias.rader@med.uni-muenchen.de.
² Division of Audiology, Department for Otorhinolaryngology, University Hospital, Ludwig-Maximilians-Universität München, Munich, Germany.
³ Dermatology Bad Soden, Bad Soden, Germany; Division of Audiological Acoustics, Department for Otorhinolaryngology, University Hospital Frankfurt, Frankfurt, Germany.
⁴ Division of Audiological Acoustics, Department for Otorhinolaryngology, University Hospital Frankfurt, Frankfurt, Germany.

PMID: 37031765
DOI: 10.1016/j.jneumeth.2023.109854

Abstract

Background: Hearing performance in cochlear implant (CI) users is variable. An objective measure which can allow a prediction of this performance is desirable. Spread of neural excitation (SoE) curves are an objective measure that can be obtained using the fitting software of cochlear implants and might be able to be used as a predictor. A novel method to interpret SoE curves is presented.

New method: Spread of excitation measurements for three recording sites were fitted using two exponential functions. An asymmetric width measure was developed, defined as the distance in mm to the point, where 25% or 50% of peak normalized amplitude was reached, for each half of the SoE separately. Also, a novel population of subjects with MED-EL CIs is used. Furthermore, speech perception (speech reception threshold, SRT) was evaluated using a matrix sentence test in a multi-source noise field.

Results: SoE width was narrowest for the basal recording site and widest for the apical recording site. Fitted SoE exponential functions were most asymmetric for the apical recording site. A significant positive correlation between sentence test SRT and SoE width at the apical recording site was found.

Comparison with existing methods: The use of an asymmetric width measure correlated strongly and positively with speech perception for apical recording sites, unlike the symmetric width measure used in previous studies. Presumably, longer electrodes allow stimulation of a more apical part of the cochlear. At the apical part of the cochlea, dendrites from a large region of the basilar membrane map to a narrow portion on the spiral ganglion, which might explain the observed asymmetry.

Conclusions: For subjects implanted with long electrode arrays, an asymmetric width measure correlates positively with apical SoE distance. However, due to lack of a sufficient amount of data, the results are currently less conclusive and need to be consolidated in a larger cohort of subjects.

Keywords: Cochlear implant; ECAP; Electric field; Exponential fitting; Spread of excitation.

MeSH terms

Cochlea
Cochlear Implantation* / methods
Cochlear Implants*
Electric Stimulation
Humans
Speech Perception*
Spiral Ganglion