Jiang C, de Rijk S R, Malliaras G G, Bance M L
Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 0AH, United Kingdom.
Division of Electrical Engineering, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom.
APL Mater. 2020 Sep 1;8(9):091102. doi: 10.1063/5.0012514.
Cochlear implants (CIs) have tremendously helped people with severe to profound hearing loss to gain access to sound and oral-verbal communication. However, the electrical stimulus in the cochlea spreads easily and widely, since the perilymph and endolymph (i.e., intracochlear fluids) are essentially electrolytes, leading to an inability to focus stimulation to discrete portions of the auditory nerve, which blurs the neural signal. Here, we characterize the complex transimpedances of human cadaveric cochleas to investigate how electrical stimulus spread is distributed from 10 Hz to 100 kHz. By using electrochemical impedance spectroscopy (EIS), both the resistive and capacitive elements of human cochleas are measured and modeled with an electrical circuit model, identifying spread-induced and spread-independent impedance components. Based on this electrical circuit model, we implement a Laplace transform to simulate the theoretical shapes of the spread signals. The model is validated by experimentally applying the simulated stimulus as a real stimulus to the cochlea and measuring the shapes of the spread signals, with relative errors of <0.6% from the model. Based on this model, we show the relationship between stimulus pulse duration and electrical stimulus spread. This EIS technique to characterize the transimpedances of human cochleas provides a new way to predict the spread signal under an arbitrary electrical stimulus, thus providing preliminary guidance to the design of CI stimuli for different CI users and coding strategies.
人工耳蜗极大地帮助了重度至极重度听力损失患者获得声音并进行口语交流。然而，由于外淋巴和内淋巴（即耳蜗内的液体）本质上是电解质，耳蜗中的电刺激容易广泛扩散，导致无法将刺激集中于听神经的离散部分，从而使神经信号模糊。在此，我们对人类尸体耳蜗的复阻抗进行表征，以研究从10赫兹到100千赫兹电刺激的扩散分布情况。通过使用电化学阻抗谱（EIS），测量并用电路模型对人类耳蜗的电阻和电容元件进行建模，识别出扩散诱导和扩散无关的阻抗成分。基于此电路模型，我们进行拉普拉斯变换以模拟扩散信号的理论形状。通过将模拟刺激作为真实刺激施加到耳蜗并测量扩散信号的形状来验证该模型，测量结果与模型的相对误差小于0.6%。基于此模型，我们展示了刺激脉冲持续时间与电刺激扩散之间的关系。这种用于表征人类耳蜗复阻抗的EIS技术为预测任意电刺激下的扩散信号提供了一种新方法，从而为不同人工耳蜗使用者的人工耳蜗刺激设计和编码策略提供初步指导。
