Kalkman Randy K, Briaire Jeroen J, Dekker David M T, Frijns Johan H M
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. 2014 Sep;315:10-24. doi: 10.1016/j.heares.2014.06.003. Epub 2014 Jun 26.
Place pitch was investigated in a computational model of the implanted human cochlea containing nerve fibres with realistic trajectories that take the variable distance between the organ of Corti and spiral ganglion into account. The model was further updated from previous studies by including fluid compartments in the modiolus and updating the electrical conductivity values of (temporal) bone and the modiolus, based on clinical data. Four different cochlear geometries are used, modelled with both lateral and perimodiolar implants, and their neural excitation patterns were examined for nerve fibres modelled with and without peripheral processes. Additionally, equations were derived from the model geometries that describe Greenwood's frequency map as a function of cochlear angle at the basilar membrane as well as at the spiral ganglion. The main findings are: (I) in the first (basal) turn of the cochlea, cochlear implant induced pitch can be predicted fairly well using the Greenwood function. (II) Beyond the first turn this pitch becomes increasingly unpredictable, greatly dependent on stimulus level, state of the cochlear neurons and the electrode's distance from the modiolus. (III) After the first turn cochlear implant induced pitch decreases as stimulus level increases, but the pitch does not reach values expected from direct spiral ganglion stimulation unless the peripheral processes are missing. (IV) Electrode contacts near the end of the spiral ganglion or deeper elicit very unpredictable pitch, with broad frequency ranges that strongly overlap with those of neighbouring contacts. (V) The characteristic place pitch for stimulation at either the organ of Corti or the spiral ganglion can be described as a function of cochlear angle by the equations presented in this paper.
在植入式人类耳蜗的计算模型中研究了位置音调，该模型包含具有实际轨迹的神经纤维，这些轨迹考虑了柯蒂氏器与螺旋神经节之间的可变距离。该模型在先前研究的基础上进一步更新，通过在蜗轴中纳入液体隔室，并根据临床数据更新（颞）骨和蜗轴的电导率值。使用了四种不同的耳蜗几何形状，对侧向和蜗周植入物进行建模，并检查了它们对有和没有外周突的神经纤维的神经兴奋模式。此外，从模型几何形状中推导出了方程，这些方程将格林伍德频率图描述为基底膜以及螺旋神经节处耳蜗角度的函数。主要发现如下：（I）在耳蜗的第一（基底）圈中，使用格林伍德函数可以相当准确地预测人工耳蜗诱发的音调。（II）在第一圈之后，这种音调变得越来越难以预测，很大程度上取决于刺激水平、耳蜗神经元的状态以及电极与蜗轴的距离。（III）在第一圈之后，人工耳蜗诱发的音调随着刺激水平的增加而降低，但除非外周突缺失，否则音调不会达到直接刺激螺旋神经节所预期的值。（IV）靠近螺旋神经节末端或更深位置的电极触点会引发非常难以预测的音调，其频率范围很宽，与相邻触点的频率范围有很大重叠。（V）本文提出的方程可以将在柯蒂氏器或螺旋神经节处刺激的特征位置音调描述为耳蜗角度的函数。
