Jeng Fuh-Cherng, Abbas Paul J, Hu Ning, Miller Charles A, Nourski Kirill V, Robinson Barbara K
School of Hearing, Speech and Language Sciences, Ohio University, Athens, OH 45701, USA.
Hear Res. 2009 Jan;247(1):47-59. doi: 10.1016/j.heares.2008.10.007. Epub 2008 Nov 5.
The electrically evoked compound action potential (ECAP) of the auditory nerve in response to amplitude-modulated pulse trains varies over time, but the response amplitudes are not linearly proportional to the level of stimulus pulses. At least two mechanisms could contribute to the deviations of the ECAP response pattern from that of the stimulus envelope. The first mechanism is time-invariant or stationary that reflects the non-linear growth of response amplitude with changes in stimulus level that is evident in the response to single pulses. This can be considered a time-invariant or stationary effect. The second mechanism is time-variant or non-stationary and reflects neural refractoriness and adaptation. The purpose of this study was to characterize the auditory nerve responses to amplitude-modulated pulse trains and also to evaluate the extent to which the stationary and non-stationary effects may contribute to those responses. ECAP amplitudes were predicted from single-pulse growth functions of the auditory nerve to account for time-invariant effects. Linear regression was performed on the measured vs. predicted ECAP amplitudes to quantify the discrepancies between the two datasets, thereby separating the influence of non-linear growth from time-varying effects on ECAP amplitudes. The results demonstrated a bandpass function of the modulated response amplitudes, with a low-cutoff modulation frequency at 300Hz and a high-cutoff modulation frequency at 800Hz, depending on the carrier pulse rate. The relative contribution of the temporal effects on ECAP amplitudes is greatest at low stimulus levels and low modulation depths.
听神经对调幅脉冲序列的电诱发复合动作电位（ECAP）会随时间变化，但其响应幅度与刺激脉冲的强度并非呈线性比例关系。至少有两种机制可能导致ECAP响应模式与刺激包络的响应模式出现偏差。第一种机制是时不变或平稳的，它反映了响应幅度随刺激强度变化的非线性增长，这在对单个脉冲的响应中很明显。这可被视为一种时不变或平稳效应。第二种机制是时变或非平稳的，反映了神经不应期和适应性。本研究的目的是描述听神经对调幅脉冲序列的响应特征，并评估平稳和非平稳效应在这些响应中可能起作用的程度。根据听神经的单脉冲增长函数预测ECAP幅度，以考虑时不变效应。对测量的和预测的ECAP幅度进行线性回归，以量化两个数据集之间的差异，从而将非线性增长的影响与随时间变化的效应在ECAP幅度上的影响区分开来。结果表明，调制响应幅度具有带通函数，根据载波脉冲率，低截止调制频率为300Hz，高截止调制频率为800Hz。时间效应在低刺激强度和低调制深度下对ECAP幅度的相对贡献最大。
