The electrically evoked compound action potential (eCAP) is a direct measure of the responsiveness of the auditory nerve to electrical stimulation from a cochlear implant (CI). CIs offer a unique opportunity to study the auditory nerve’s electrophysiological behavior in individual human subjects over time. In order to understand exactly how the eCAP relates to the condition of the auditory nerve, it is crucial to compare changes in the eCAP over time in a controlled model of deafness-induced auditory nerve degeneration. In the present study, 10 normal-hearing young adult guinea pigs were implanted and deafened 4 weeks later, so that the effect of deafening could be monitored within-subject over time. Following implantation, but before deafening, most examined eCAP characteristics significantly changed, suggesting increasing excitation efficacy (e.g., higher maximum amplitude, lower threshold, shorter latency). Conversely, inter-phase gap (IPG) effects on these measures – within-subject difference measures that have been shown to correlate well with auditory nerve survival – did not vary for most eCAP characteristics. After deafening, we observed an initial increase in excitability (steeper slope of the eCAP amplitude growth function (AGF), lower threshold, shorter latency and peak width) which typically returned to normal-hearing levels within a week, after which a slower process, probably reflecting spiral ganglion cell loss, took place over the remaining 6 weeks (e.g., decrease in maximum amplitude, AGF slope, peak area, and IPG effect for AGF slope; increase in IPG effect for latency). Our results suggest that gradual changes in peak width and latency reflect the rate of neural degeneration, while peak area, maximum amplitude, and AGF slope reflect neural population size, which may be valuable for clinical diagnostics.

电诱发复合动作电位 (eCAP) 是听觉神经对来自人工耳蜗 (CI) 的电刺激的反应性的直接测量。CI 提供了一个独特的机会来研究随着时间的推移，个体人类受试者的听觉神经电生理行为。为了准确了解 eCAP 与听觉神经状况的关系，在耳聋引起的听觉神经退化的受控模型中比较 eCAP 随时间的变化至关重要。在本研究中，10 只听力正常的年轻成年豚鼠被植入并在 4 周后耳聋，以便随着时间的推移在受试者体内监测耳聋的效果。植入后，但在震耳欲聋之前，大多数检查的 eCAP 特征发生了显着变化，表明激发效率增加（例如 g.，更高的最大幅度，更低的阈值，更短的延迟）。相反，相间间隙 (IPG) 对这些测量的影响——已显示与听觉神经存活密切相关的受试者内差异测量——对于大多数 eCAP 特征没有变化。震耳欲聋后，我们观察到兴奋性的初始增加（eCAP 振幅增长函数 (AGF) 的斜率更陡、阈值更低、潜伏期更短和峰宽）通常在一周内恢复到正常听力水平，此后过程变慢，可能反映螺旋神经节细胞丢失，发生在剩余的 6 周内（例如，最大幅度、AGF 斜率、峰面积和 AGF 斜率的 IPG 效应降低；潜伏期 IPG 效应增加）。