Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Utrecht University, Room G.02.531, P.O. Box 85500, 3508 GA, Utrecht, the Netherlands.
UMC Utrecht Brain Center, Utrecht University, Utrecht, the Netherlands.
J Assoc Res Otolaryngol. 2022 Dec;23(6):721-738. doi: 10.1007/s10162-022-00864-0. Epub 2022 Aug 10.
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）是对人工耳蜗（CI）电刺激的听神经反应的直接测量。CI 为研究个体人类受试者的听神经电生理行为随时间的变化提供了独特的机会。为了准确了解 eCAP 与听神经状况的关系，在耳聋诱导的听神经变性的对照模型中，比较 eCAP 随时间的变化至关重要。在本研究中，10 只正常听力的成年豚鼠被植入并在 4 周后失聪，以便在时间内进行对照监测失聪对 eCAP 的影响。植入后但在失聪前，大多数检查的 eCAP 特征显著改变，这表明兴奋效率增加（例如，更高的最大幅度、更低的阈值、更短的潜伏期）。相反，相位间隔（IPG）对这些措施的影响——已被证明与听神经存活密切相关的受试者内差异措施——对于大多数 eCAP 特征而言并没有变化。失聪后，我们观察到兴奋性的初始增加（eCAP 幅度增长函数（AGF）的斜率更陡、阈值更低、潜伏期和峰宽更短），这通常在一周内恢复到正常听力水平，然后是一个更慢的过程，可能反映螺旋神经节细胞的丧失，在其余的 6 周内发生（例如，最大幅度、AGF 斜率、峰值面积和 AGF 斜率的 IPG 效应降低；潜伏期的 IPG 效应增加）。我们的结果表明，峰宽和潜伏期的逐渐变化反映了神经变性的速度，而峰值面积、最大幅度和 AGF 斜率反映了神经群体的大小，这对于临床诊断可能很有价值。
