Sato Mika, Baumhoff Peter, Kral Andrej
Institute of AudioNeuroTechnology and Department of Experimental Otology, ENT Clinics, Hannover Medical School, 30625 Hannover, Germany
Institute of AudioNeuroTechnology and Department of Experimental Otology, ENT Clinics, Hannover Medical School, 30625 Hannover, Germany.
J Neurosci. 2016 Jan 6;36(1):54-64. doi: 10.1523/JNEUROSCI.2968-15.2016.
Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of the electrical stimulus, provided these are < 12 kHz. The slope of the rate-level functions of the neurons in the deafened condition was steeper and the firing rate was higher than in the hearing condition at those sites that were activated in the two conditions. Finally, in a monopolar stimulation configuration, the differences between hearing status conditions were smaller than in the narrower (bipolar) configurations.
Stimulation with cochlear implants and hearing aids is becoming more widely clinically used in subjects with residual hearing. The neurophysiological characteristics underlying electroacoustic stimulation and the mechanism of its benefit remain unclear. The present study directly demonstrates that cochlear implantation does not interfere with the normal mechanical and physiological function of the cochlea. For the first time, it double-dissociates the electrical responses of hair cells (electrophonic responses) from responses of the auditory nerve fibers (electroneural responses), with separate excited cochlear locations in the same animals. We describe the condition in which these two responses spatially overlap. Finally, the study implicates that using the clinical characteristics of stimulation makes electrophonic responses unlikely in implanted subjects.
对有残余听力的受试者进行电声刺激在临床实践中的应用越来越广泛。然而，对于听觉耳蜗中电诱发反应的特性却知之甚少。在本研究中，听力正常的豚鼠耳蜗通过蜗窗进行人工耳蜗植入，听力无明显损失。利用中脑单位活动记录，我们能够研究由声刺激确定的整个音频区域的兴奋模式。在保留人工耳蜗和中脑多电极阵列的情况下，对耳朵进行药物致聋，并在致聋状态下重复电刺激。结果表明，除了直接的神经元（电神经）刺激外，在听觉耳蜗中，对应于电刺激的主要时间频率成分的耳蜗部位会发生毛细胞兴奋（“电声反应”），前提是这些频率小于12千赫兹。在两种状态下均被激活的部位，致聋状态下神经元的发放率-强度函数斜率更陡，发放率高于听力状态。最后，在单极刺激配置中，听力状态之间的差异小于在较窄（双极）配置中的差异。
人工耳蜗和助听器刺激在有残余听力的受试者中的临床应用越来越广泛。电声刺激的神经生理学特征及其益处的机制仍不清楚。本研究直接表明人工耳蜗植入不会干扰耳蜗的正常机械和生理功能。首次在同一动物中，将毛细胞的电反应（电声反应）与听神经纤维的反应（电神经反应）进行了双重分离，且兴奋的耳蜗位置不同。我们描述了这两种反应在空间上重叠的情况。最后，该研究表明，利用刺激的临床特征会使植入受试者不太可能出现电声反应。
