Department of Speech and Hearing Sciences, University of Washington, Seattle, Washington 98105, USA.
Ear Hear. 2011 Jul-Aug;32(4):436-44. doi: 10.1097/AUD.0b013e3181ff33ab.
The goal of this study was to compare cochlear implant behavioral measures and electrically evoked auditory brain stem responses (EABRs) obtained with a spatially focused electrode configuration. It has been shown previously that channels with high thresholds, when measured with the tripolar configuration, exhibit relatively broad psychophysical tuning curves. The elevated threshold and degraded spatial/spectral selectivity of such channels are consistent with a poor electrode-neuron interface, defined as suboptimal electrode placement or reduced nerve survival. However, the psychophysical methods required to obtain these data are time intensive and may not be practical during a clinical mapping session, especially for young children. Here, we have extended the previous investigation to determine whether a physiological approach could provide a similar assessment of channel functionality. We hypothesized that, in accordance with the perceptual measures, higher EABR thresholds would correlate with steeper EABR amplitude growth functions, reflecting a degraded electrode-neuron interface.
Data were collected from six cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. EABRs were obtained in each subject for the two channels having the highest and lowest tripolar (σ = 1 or 0.9) behavioral threshold. Evoked potentials were measured with both the monopolar (σ = 0) and a more focused partial tripolar (σ ≥ 0.50) configuration.
Consistent with previous studies, EABR thresholds were highly and positively correlated with behavioral thresholds obtained with both the monopolar and partial tripolar configurations. The Wave V amplitude growth functions with increasing stimulus level showed the predicted effect of shallower growth for the partial tripolar than for the monopolar configuration, but this was observed only for the low-threshold channels. In contrast, high-threshold channels showed the opposite effect; steeper growth functions were seen for the partial tripolar configuration.
These results suggest that behavioral thresholds or EABRs measured with a restricted stimulus can be used to identify potentially impaired cochlear implant channels. Channels having high thresholds and steep growth functions would likely not activate the appropriate spatially restricted region of the cochlea, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.
本研究旨在比较采用空间聚焦电极配置获得的人工耳蜗行为测量值和电诱发听觉脑干反应（EABR）。先前已经表明，当采用三极配置测量时，具有较高阈值的通道表现出相对较宽的心理物理调谐曲线。这些通道的高阈值和较差的空间/光谱选择性与较差的电极-神经元界面一致，定义为电极放置不理想或神经存活减少。然而，获得这些数据所需的心理物理方法耗时且在临床映射会话期间可能不切实际，尤其是对于年幼的儿童。在这里，我们扩展了先前的研究，以确定生理方法是否可以提供对通道功能的类似评估。我们假设，与感知测量一致，较高的 EABR 阈值将与更陡峭的 EABR 幅度增长函数相关，反映出电极-神经元界面的恶化。
数据来自六名植入 HiRes 90k 人工耳蜗（先进仿生公司）的人工耳蜗植入者。使用部分三极配置获得刺激的单通道阈值和最舒适的听力水平，该配置中，来自中心有源电极的一部分电流（σ）通过两个相邻电极返回，其余电流通过远处的无关电极返回。对于具有最高和最低三极（σ=1 或 0.9）行为阈值的两个通道，在每个受试者中获得 EABR。使用单极（σ=0）和更聚焦的部分三极（σ≥0.50）配置获得诱发电位。
与先前的研究一致，EABR 阈值与使用单极和部分三极配置获得的行为阈值高度正相关。随着刺激水平的增加，Wave V 幅度增长函数显示出部分三极比单极配置的增长更浅的预期效应，但仅观察到低阈值通道。相比之下，高阈值通道显示出相反的效果；部分三极配置的增长函数更陡峭。
这些结果表明，使用受限刺激测量的行为阈值或 EABR 可用于识别潜在受损的人工耳蜗通道。具有高阈值和陡峭增长函数的通道可能无法激活耳蜗的适当空间限制区域，从而导致感知不佳。作为临床工具，快速识别受损通道可以导致针对患者的映射策略，并改善言语和音乐感知。
