Parkins C W, Colombo J
Division of Otolaryngology, University of Rochester School of Medicine and Dentistry, New York 14642.
Hear Res. 1987 Dec 31;31(3):267-85. doi: 10.1016/0378-5955(87)90196-1.
Single auditory-nerve neuron thresholds were studied in sensory-deafened squirrel monkeys to determine the effects of electrical stimulus shape and frequency on single-neuron thresholds. Frequency was separated into its components, pulse width and pulse rate, which were analyzed separately. Square and sinusoidal pulse shapes were compared. There were no or questionably significant threshold differences in charge per phase between sinusoidal and square pulses of the same pulse width. There was a small (less than 0.5 dB) but significant threshold advantage for 200 microseconds/phase pulses delivered at low pulse rates (156 pps) compared to higher pulse rates (625 pps and 2500 pps). Pulse width was demonstrated to be the prime determinant of single-neuron threshold, resulting in strength-duration curves similar to other mammalian myelinated neurons, but with longer chronaxies. The most efficient electrical stimulus pulse width to use for cochlear implant stimulation was determined to be 100 microseconds/phase. This pulse width delivers the lowest charge/phase at threshold. The single-neuron strength-duration curves were compared to strength-duration curves of a computer model based on the specific anatomy of auditory-nerve neurons. The membrane capacitance and resulting chronaxie of the model can be varied by altering the length of the unmyelinated termination of the neuron, representing the unmyelinated portion of the neuron between the habenula perforata and the hair cell. This unmyelinated segment of the auditory-nerve neuron may be subject to aminoglycoside damage. Simulating a 10 micron unmyelinated termination for this model neuron produces a strength-duration curve that closely fits the single-neuron data obtained from aminoglycoside deafened animals. Both the model and the single-neuron strength-duration curves differ significantly from behavioral threshold data obtained from monkeys and humans with cochlear implants. This discrepancy can best be explained by the involvement of higher level neurologic processes in the behavioral responses. These findings suggest that the basic principles of neural membrane function must be considered in developing or analyzing electrical stimulation strategies for cochlear prostheses if the appropriate stimulation of frequency specific populations of auditory-nerve neurons is the objective.
在感觉性耳聋的松鼠猴中研究了单个听神经神经元的阈值，以确定电刺激形状和频率对单个神经元阈值的影响。频率被分解为其组成部分，即脉冲宽度和脉冲速率，并分别进行分析。比较了方形和正弦形脉冲形状。相同脉冲宽度的正弦脉冲和方形脉冲每相电荷之间没有或存在可疑的显著阈值差异。与较高脉冲速率（625次/秒和2500次/秒）相比，以低脉冲速率（156次/秒）传递的200微秒/相脉冲具有小（小于0.5分贝）但显著的阈值优势。脉冲宽度被证明是单个神经元阈值的主要决定因素，产生的强度-持续时间曲线与其他哺乳动物有髓神经元相似，但时值更长。确定用于人工耳蜗刺激的最有效电刺激脉冲宽度为100微秒/相。该脉冲宽度在阈值时传递最低的每相电荷。将单个神经元的强度-持续时间曲线与基于听神经神经元特定解剖结构的计算机模型的强度-持续时间曲线进行了比较。通过改变神经元无髓鞘终末的长度可以改变模型的膜电容及时值，该长度代表神经元在小孔 habenula 和毛细胞之间的无髓鞘部分。听神经神经元的这个无髓鞘段可能会受到氨基糖苷类药物的损伤。为该模型神经元模拟一个10微米的无髓鞘终末会产生一条强度-持续时间曲线，该曲线与从氨基糖苷类药物致聋动物获得的单个神经元数据紧密拟合。模型和单个神经元的强度-持续时间曲线均与从植入人工耳蜗的猴子和人类获得的行为阈值数据有显著差异。这种差异最好用行为反应中更高层次神经过程的参与来解释。这些发现表明，如果目标是适当刺激听神经神经元的频率特异性群体，那么在开发或分析人工耳蜗的电刺激策略时必须考虑神经膜功能的基本原理。
