ENT-department, Leiden University Medical Centre, PO box 9600, 2300, RC, Leiden, the Netherlands.
ENT-department, Leiden University Medical Centre, PO box 9600, 2300, RC, Leiden, the Netherlands; Leiden Institute for Brain and Cognition, PO box 9600, 2300, RC, Leiden, the Netherlands.
Hear Res. 2022 Mar 1;415:108413. doi: 10.1016/j.heares.2021.108413. Epub 2021 Dec 9.
The main aim of this computational modelling study was to test the validity of the hypothesis that sensitivity to the polarity of cochlear implant stimulation can be interpreted as a measure of neural health. For this purpose, the effects of stimulus polarity on neural excitation patterns were investigated in a volume conduction model of the implanted human cochlea, which was coupled with a deterministic active nerve fibre model based on characteristics of human auditory neurons. The nerve fibres were modelled in three stages of neural degeneration: intact, with shortened peripheral terminal nodes and with complete loss of the peripheral processes. The model simulated neural responses to monophasic, biphasic, triphasic and pseudomonophasic pulses of both polarities. Polarity sensitivity was quantified as the so-called polarity effect (PE), which is defined as the dB difference between cathodic and anodic thresholds. Results showed that anodic pulses mostly excited the auditory neurons in their central axons, while cathodic stimuli generally excited neurons in their peripheral processes or near their cell bodies. As a consequence, cathodic thresholds were more affected by neural degeneration than anodic thresholds. Neural degeneration did not have a consistent effect on the modelled PE values, though there were notable effects of electrode contact insertion angle and distance from the modiolus. Furthermore, determining PE values using charge-balanced multiphasic pulses as approximations of monophasic stimuli produced different results than those obtained with true monophasic pulses, at a degree that depended on the specific pulse shape; in general, pulses with lower secondary phase amplitudes showed polarity sensitivities closer to those obtained with true monophasic pulses. The main conclusion of this study is that polarity sensitivity is not a reliable indicator of neural health; neural degeneration affects simulated polarity sensitivity, but its effect is not consistently related to the degree of degeneration. Polarity sensitivity is not simply a product of the state of the neurons, but also depends on spatial factors.
本计算建模研究的主要目的是检验以下假设的有效性，即对耳蜗植入刺激极性的敏感性可以解释为神经健康的衡量标准。为此，在植入人耳蜗的容积传导模型中研究了刺激极性对神经兴奋模式的影响，该模型与基于人类听觉神经元特性的确定性活性神经纤维模型耦合。神经纤维在三个神经退化阶段进行建模：完整、末梢节点缩短和外周过程完全丧失。该模型模拟了单极、双极、三极和伪单极脉冲对两种极性的神经反应。极性敏感性被量化为所谓的极性效应 (PE)，其定义为阴极和阳极阈值之间的 dB 差异。结果表明，阳极脉冲主要激发听觉神经元的中央轴突，而阴极刺激通常激发神经元的外周过程或靠近细胞体。因此，阴极阈值比阳极阈值更容易受到神经退化的影响。神经退化对模型化的 PE 值没有一致的影响，尽管电极接触插入角度和距蜗轴的距离有明显的影响。此外，使用电荷平衡多相脉冲作为单极刺激的近似值来确定 PE 值会产生与使用真正单极脉冲获得的结果不同的结果，其程度取决于特定的脉冲形状；一般来说，次级相位幅度较低的脉冲表现出与真正单极脉冲获得的极性敏感性更接近。本研究的主要结论是，极性敏感性不是神经健康的可靠指标；神经退化会影响模拟的极性敏感性，但它的影响与退化程度没有一致的关系。极性敏感性不仅仅是神经元状态的产物，还取决于空间因素。
Zotero 插件