Evaluating and comparing behavioural and electrophysiological estimates of neural health in cochlear implant users

• DOI: 10.31234/osf.io/2kp7x
• Publication Date: 2020-03-03T11:54:40Z
• Authors: Tim Brochier; Francois Guerit; Charlotte Garcia; John M. Deeks; Manohar L. Bance; Robert P. Carlyon
• Keywords: bepress|Engineering; computational modelling; Guinea Pigs; 01 natural sciences; bepress|Life Sciences|Neuroscience and Neurobiology; 03 medical and health sciences; 0302 clinical medicine; cochlear implants; psychophysics; multi-pulse integration; neural survival; 0103 physical sciences; Animals; Computer Simulation; PsyArXiv|Engineering Psychology; polarity effect; Cochlear Nerve; bepress|Life Sciences|Neuroscience and Neurobiology|Other Neuroscience and Neurobiology; inter-phase gap; ECAP; Reproducibility of Results; Other Neuroscience and Neurobiology; Engineering Psychology; neural health; Cochlear Implants; PsyArXiv|Neuroscience; PsyArXiv|Neuroscience|Other Neuroscience and Neurobiology; Auditory Perception; Neuroscience; Research Article

Variations in neural health along the cochlea can degrade the spectral and temporal representation of sounds conveyed by cochlear implants (CIs) . We evaluated and compared several methods that have been proposed as estimates of neural health patterns, in order to explore the extent to which the different measures provide converging and consistent neural health estimates. All measures were obtained from the same 11 users of the Cochlear Corporation CI. The two behavioural measures were multipulse integration (MPI) and the polarity effect (PE), both measured on each of seven electrodes per subject. MPI was measured as the difference between thresholds at 80-pps and 1000-pps, and PE as the difference in thresholds between cathodic- and anodic-centred quadraphasic (QP) 80-pps pulse trains. It has been proposed that good neural health corresponds to a large MPI and to a large negative PE (lower thresholds for cathodic than anodic pulses). The electrophysiological measure was the effect of interphase gap (IPG) on the offset of the ECAP amplitude growth function (AGF), which has been correlated with spiral ganglion nerve density in guinea pigs. This “IPG offset” was obtained on the same subset of electrodes as for the behavioural measures. Despite high test-retest reliability, there were no significant correlations between the neural health estimates for either within-subject comparisons across the electrode array, or between-subjects comparisons of the means. A phenomenological model of a population of spiral ganglion neurons was then used to investigate physiological mechanisms that might underlie the different neural health estimates. The combined experimental and modelling results provide evidence that PE, MPI, and IPG offset reflect different characteristics of the electrode-neural interface.