Chung Yoojin, Buechel Brian D, Sunwoo Woongsang, Wagner Joseph D, Delgutte Bertrand
Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA, 02114, USA.
Department of Otolaryngology, Harvard Medical School, Boston, MA, 02115, USA.
J Assoc Res Otolaryngol. 2019 Feb;20(1):37-56. doi: 10.1007/s10162-018-00708-w. Epub 2019 Jan 8.
Users of cochlear implant (CI) face challenges in everyday situations such as understanding conversations in noise, even with CIs in both ears. These challenges are related to difficulties with tasks that require fine temporal processing such as discrimination of pulse rates or interaural time differences (ITD), a major cue for sound localization. The degradation in temporal processing and ITD sensitivity are especially acute in those who lost hearing in early childhood. Here, we characterized temporal coding and ITD sensitivity of single neurons in a novel animal model of early-onset deafness. Rabbits were deafened as neonates and deprived of auditory stimulation until they reached adult age when single-unit recordings from the auditory midbrain were made chronically using an unanesthetized preparation. The results are compared to measurements from adult-deafened rabbits with normal auditory development to understand the effect of early-onset deafness on neural temporal coding and ITD sensitivity. Neurons in the inferior colliculus (IC) of early-deafened rabbits were less likely to show sustained, excitatory responses to pulse train stimulation and more likely to show suppressive responses compared to neurons in adult-deaf animals. Fewer neurons showed synchronized responses to pulse trains at any rate in the early-deaf group. In addition, fewer neurons showed significant ITD sensitivity in their overall firing rate in the early-deaf group compared to adult-deaf animals. Neural ITD discrimination thresholds in the early-deaf group were poorer than thresholds in adult-deaf group, especially at high pulse rates. The overall degradation in neural ITD sensitivity is consistent with the difficulties encountered by human CI users with early-onset hearing loss. These results lay the groundwork for investigating whether the degradations in temporal coding and ITD sensitivity observed in early-deaf animals can be reversed by appropriate CI stimulation during development.
人工耳蜗（CI）使用者在日常情况下面临挑战，例如即便双耳都植入了人工耳蜗，在嘈杂环境中理解对话也有困难。这些挑战与需要精细时间处理的任务的困难有关，比如辨别脉搏率或双耳时间差（ITD），而ITD是声音定位的一个主要线索。时间处理能力和ITD敏感性的退化在幼儿期失聪的人群中尤为严重。在此，我们在一种新的早发性耳聋动物模型中，对单个神经元的时间编码和ITD敏感性进行了表征。兔子在新生期致聋，并在成年前一直被剥夺听觉刺激，成年后在未麻醉的状态下长期进行听觉中脑的单单位记录。将结果与听觉发育正常的成年致聋兔子的测量结果进行比较，以了解早发性耳聋对神经时间编码和ITD敏感性的影响。与成年致聋动物的神经元相比，早发性耳聋兔子下丘（IC）中的神经元对脉冲序列刺激持续产生兴奋性反应的可能性较小，而更有可能表现出抑制性反应。在早发性耳聋组中，无论频率如何，对脉冲序列表现出同步反应的神经元较少。此外，与成年致聋动物相比，早发性耳聋组中在总体放电率方面表现出显著ITD敏感性的神经元较少。早发性耳聋组的神经ITD辨别阈值比成年致聋组的阈值更差，尤其是在高脉冲频率时。神经ITD敏感性的总体退化与早发性听力损失的人类人工耳蜗使用者所遇到的困难是一致的。这些结果为研究在发育过程中通过适当的人工耳蜗刺激能否逆转早发性耳聋动物中观察到的时间编码和ITD敏感性退化奠定了基础。
