Examining the ElectroNeural Interface of Cochlear

Authors: Christopher J Long Timothy A Holden Gary H McClelland Wendy S Parkinson Clough Shelton David C Kelsall Zachary M Smith

Publish Date: 2014/01/30

Volume: 15, Issue: 2, Pages: 293-304

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Abstract

This study examines the relationship between focusedstimulation thresholds electrode positions and speech understanding in deaf subjects treated with a cochlear implant CI Focused stimulation is more selective than monopolar stimulation which excites broad regions of the cochlea so may be more sensitive as a probe of neural survival patterns Focused thresholds are on average higher and more variable across electrodes than monopolar thresholds We presume that relatively high focused thresholds are the result of larger distances between the electrodes and the neurons Two factors are likely to contribute to this distance 1 the physical position of electrodes relative to the modiolus where the excitable auditory neurons are normally located and 2 the pattern of neural survival along the length of the cochlea since local holes in the neural population will increase the distance between an electrode and the nearest neurons Electrodetomodiolus distance was measured from highresolution CT scans of the cochleae of CI users whose focusedstimulation thresholds were also measured A hierarchical set of linear models of electrodetomodiolus distance versus threshold showed a significant increase in threshold with electrodetomodiolus distance average slope = 11 dB/mm The residual of these models was hypothesized to reflect neural survival in each subject Consonant–Nucleus–Consonant CNC word scores were significantly correlated with the withinsubject variance of threshold r 2 = 082 but not with withinsubject variance of electrode distance r 2 = 003 Speech understanding also significantly correlated with how well distance explained each subject’s threshold data r 2 = 063 That is subjects with focused thresholds that were well described by electrode position had better speech scores Our results suggest that speech understanding is highly impacted by individual patterns of neural survival and that these patterns manifest themselves in how well or poorly electrode position predicts focused thresholdsCJL ZMS WSP are employed by Cochlear Ltd We thank the patients for their hard work the audiologists at the clinical study sites for programming and data collection Chris van den Honert for numerous contributions and two anonymous reviewers for their useful suggestions TAH acknowledges the support of the National Institutes of Health National Institute on Deafness and Communication Disorders R01 DC00581 and R01 DC009010

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