Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School, Boston, Massachusetts, USA.
Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA.
Ear Hear. 2020 Jul/Aug;41(4):948-960. doi: 10.1097/AUD.0000000000000827.
The primary objective of this study was to quantify differences in evoked potential correlates of spiral ganglion neuron (SGN) density between younger and older individuals with cochlear implants (CIs) using the electrically evoked compound action potential (ECAP). In human temporal bone studies and in animal models, SGN density is the lowest in older subjects and in those who experienced long durations of deafness during life. SGN density also varies as a function of age at implantation and hearing loss etiology. Taken together, it is likely that younger listeners who were deafened and implanted during childhood have denser populations of SGNs than older individuals who were deafened and implanted later in life. In animals, ECAP amplitudes, amplitude growth function (AGF) slopes, and their sensitivity to stimulus interphase gap (IPG) are predictive of SGN density. The authors hypothesized that younger listeners who were deafened and implanted as children would demonstrate larger ECAP amplitudes, steeper AGF slopes, and greater IPG sensitivity than older, adult-deafened and implanted listeners.
Data were obtained from 22 implanted ears (18 individuals). Thirteen ears (9 individuals) were deafened and implanted as children (child-implanted group), and nine ears (9 individuals) were deafened and implanted as adults (adult-implanted group). The groups differed significantly on a number of demographic variables that are implicitly related to SGN density: (1) chronological age; (2) age at implantation; and (3) duration of preimplantation hearing loss. ECAP amplitudes, AGF linear slopes, and thresholds were assessed on a subset of electrodes in each ear in response to two IPGs (7 and 30 µsec). Speech recognition was assessed using a medial vowel identification task.
Compared with the adult-implanted listeners, individuals in the child-implanted group demonstrated larger changes in ECAP amplitude when the IPG of the stimulus was increased from 7 to 30 µsec (i.e., greater IPG sensitivity). On average, child-implanted participants also had larger ECAP amplitudes and steeper AGF linear slopes than the adult-implanted participants, irrespective of IPG. IPG sensitivity for AGF linear slope and ECAP threshold did not differ between age groups. Vowel recognition performance was not correlated with any of the ECAP measures assessed in this study.
The results of this study support the theory that young CI listeners who were deafened and implanted during childhood may have denser neural populations than older listeners who were deafened and implanted as adults. Potential between-group differences in SGN integrity emphasize a need to investigate optimized CI programming parameters for younger and older listeners.
本研究的主要目的是使用电诱发复合动作电位（ECAP）量化年轻和老年人工耳蜗植入（CI）患者螺旋神经节神经元（SGN）密度的诱发电位相关性差异。在人类颞骨研究和动物模型中，SGN 密度在老年人和生命中经历长时间耳聋的人中最低。SGN 密度也随植入时的年龄和听力损失病因而变化。总的来说，在童年时期失聪并植入的年轻听众的 SGN 密度可能比晚年失聪并植入的听众更高。在动物中，ECAP 幅度、幅度增长函数（AGF）斜率及其对刺激相间间隙（IPG）的敏感性可预测 SGN 密度。作者假设，在童年时期失聪并植入的年轻听众的 ECAP 幅度更大，AGF 斜率更陡，对 IPG 的敏感性更高，而成年失聪并植入的听众则较低。
数据来自 22 个植入耳朵（18 个人）。13 只耳朵（9 人）在儿童时期失聪并植入（儿童植入组），9 只耳朵（9 人）在成年时期失聪并植入（成年植入组）。这两个组在许多与 SGN 密度有关的人口统计学变量上存在显著差异：（1）年龄；（2）植入年龄；（3）植入前听力损失的持续时间。使用两种 IPG（7 和 30 µsec）在每个耳朵的一组电极上评估 ECAP 幅度、AGF 线性斜率和阈值。使用中元音识别任务评估语音识别。
与成年植入者相比，在 IPG 从 7 µsec 增加到 30 µsec 时，儿童植入者的 ECAP 幅度变化更大（即对 IPG 的敏感性更高）。平均而言，儿童植入组的 ECAP 幅度和 AGF 线性斜率也大于成年植入组，与 IPG 无关。AGF 线性斜率和 ECAP 阈值的 IPG 敏感性在年龄组之间没有差异。元音识别性能与本研究评估的任何 ECAP 测量值均无关。
本研究结果支持这样一种理论，即在童年时期失聪并植入人工耳蜗的年轻 CI 患者可能比成年时期失聪并植入人工耳蜗的患者具有更密集的神经群体。SGN 完整性方面的潜在组间差异强调需要为年轻和老年患者研究优化的 CI 编程参数。
