Long Christopher J, Holden Timothy A, McClelland Gary H, Parkinson Wendy S, Shelton Clough, Kelsall David C, Smith Zachary M
Research and Technology Labs, Cochlear Ltd., 13059 E. Peakview Avenue, Centennial, CO, 80111, USA,
J Assoc Res Otolaryngol. 2014 Apr;15(2):293-304. doi: 10.1007/s10162-013-0437-5. Epub 2014 Jan 30.
This study examines the relationship between focused-stimulation 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. Electrode-to-modiolus distance was measured from high-resolution CT scans of the cochleae of CI users whose focused-stimulation thresholds were also measured. A hierarchical set of linear models of electrode-to-modiolus distance versus threshold showed a significant increase in threshold with electrode-to-modiolus 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 within-subject variance of threshold (r(2) = 0.82), but not with within-subject variance of electrode distance (r(2) = 0.03). Speech understanding also significantly correlated with how well distance explained each subject's threshold data (r(2) = 0.63). 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 thresholds.
本研究探讨了接受人工耳蜗（CI）治疗的聋人受试者中，聚焦刺激阈值、电极位置与言语理解之间的关系。聚焦刺激比单极刺激更具选择性，单极刺激会激发耳蜗的广泛区域，因此作为神经存活模式的探测手段，聚焦刺激可能更敏感。聚焦阈值平均比单极阈值更高，且在不同电极间变化更大。我们推测，相对较高的聚焦阈值是电极与神经元之间距离较大的结果。有两个因素可能导致这种距离：（1）电极相对于蜗轴的物理位置，可兴奋的听觉神经元通常位于蜗轴；（2）沿耳蜗长度的神经存活模式，因为神经群体中的局部空洞会增加电极与最近神经元之间的距离。通过对聚焦刺激阈值也已测量的CI使用者的耳蜗进行高分辨率CT扫描，测量电极到蜗轴的距离。一组分层的电极到蜗轴距离与阈值的线性模型显示，阈值随电极到蜗轴距离显著增加（平均斜率 = 11 dB/mm）。这些模型的残差被假设为反映每个受试者的神经存活情况。辅音 - 元音 - 辅音（CNC）单词得分与阈值的受试者内方差显著相关（r(2) = 0.82），但与电极距离的受试者内方差无关（r(2) = 0.03）。言语理解也与距离对每个受试者阈值数据的解释程度显著相关（r(2) = 0.63）。也就是说，聚焦阈值能被电极位置很好描述的受试者，言语得分更高。我们的结果表明，言语理解受到个体神经存活模式的高度影响，并且这些模式通过电极位置预测聚焦阈值的好坏得以体现。
