Cambridge Hearing Group, MRC Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK.
Cambridge Hearing Group, Cambridge University Hospitals Foundation Trust, Hills Road, Cambridge, CB2 0QQ, UK.
J Assoc Res Otolaryngol. 2021 Feb;22(1):67-80. doi: 10.1007/s10162-020-00773-0. Epub 2020 Nov 4.
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 one electrophysiological measure and two behavioural measures 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 neuron density in guinea pigs. This 'IPG offset' was obtained on the same subset of electrodes used 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-subject 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 may reflect different characteristics of the electrode-neural interface.
耳蜗内神经健康的变化可能会降低人工耳蜗（CI）传递声音的频谱和时程表现。我们评估并比较了一种电生理测量和两种行为测量，它们被提出作为神经健康模式的估计方法，以探讨不同方法在多大程度上提供了收敛和一致的神经健康估计。所有测量均来自科利尔公司 CI 的 11 名相同使用者。两种行为测量是多脉冲整合（MPI）和极性效应（PE），均在每个受试者的七个电极上进行测量。MPI 测量为 80pps 和 1000pps 阈值之间的差异，PE 测量为阴极和阳极中心四相（QP）80pps 脉冲串之间阈值的差异。据认为，良好的神经健康对应于较大的 MPI 和较大的负 PE（阴极脉冲的阈值低于阳极脉冲）。电生理测量是相间间隙（IPG）对 ECAP 幅度增长函数（AGF）偏移的影响，该测量与豚鼠螺旋神经节神经元密度相关。该“IPG 偏移”是在用于行为测量的相同电极子集上获得的。尽管具有高测试-重测可靠性，但在电极阵列内的个体间比较或个体间平均值的比较中，神经健康估计之间均无显著相关性。然后使用群体螺旋神经节神经元的现象学模型来研究可能是不同神经健康估计基础的生理机制。综合实验和建模结果表明，PE、MPI 和 IPG 偏移可能反映了电极-神经界面的不同特征。
