LePage E L
J Acoust Soc Am. 1987 Jul;82(1):139-54. doi: 10.1121/1.395557.
A displacement-sensitive capacitive probe technique was used in the first turn of guinea pig cochleas to examine whether the motion of the basilar membrane includes a displacement component analogous to the dc receptor potentials of the hair cells. Such a "dc" component apparently exists. At a given location on the basilar membrane, its direction toward scala vestibuli (SV) or scala tympani (ST) varies systematically with frequency of the acoustic stimulus. Furthermore, it appears to consist of two parts: a small asymmetric offset response to each gated tone burst plus a progressive shift of the basilar membrane from its previous position. The mean position shift is cumulative, increasing with successive tone bursts. The amplitude of the immediate offset response, when plotted as a function of frequency, appears to exhibit a trimodal pattern. This displacement offset is toward SV at the characteristic frequency (CF) of the location of the probe, while at frequencies either above or below the CF the offset is relatively larger, and toward ST. The mechanical motion of the basilar membrane therefore appears to contain the basis for lateral suppression. The cumulative mean position shift, however, appears to peak toward ST at the apical end of the traveling wave envelope and appears to be associated with a resonance, not of the basilar membrane motion directly, but coupled to it. The summating potential, measured concurrently at the round window, shows a more broadly tuned peak just above the CF of the position of the probe. This seems to correspond to the peak at the CF of the mechanical bias. As the preparation deteriorates, the best frequency of the vibratory displacement response decreases to about a half-octave below the original CF. There is a corresponding decrease in the frequency of the peaks of the trimodal pattern of the asymmetric responses to tone bursts. The trimodal pattern also broadens. In previous experiments the basilar membrane has been forced to move in response to a low-frequency biasing tone. The sensitivity to high-frequency stimuli varies in phase with the biasing tone. The amplitudes of slow movement in these earlier experiments and in the present experiments are of the same order of magnitude. This suggests strongly that the cumulative shift toward ST to a high-frequency acoustic stimulus constitutes a substantial controlling bias on the sensitivity of the cochlea in that same high-frequency region. Its effect will be to reduce the slope of neural rate-level functions on the high-frequency side of CF.
在豚鼠耳蜗的第一圈中使用了一种位移敏感电容式探头技术，以检查基底膜的运动是否包含类似于毛细胞直流受体电位的位移成分。这样的“直流”成分显然存在。在基底膜的给定位置，其朝向前庭阶（SV）或鼓阶（ST）的方向随声刺激频率而系统变化。此外，它似乎由两部分组成：对每个门控音爆的小的不对称偏移响应加上基底膜相对于其先前位置的渐进性位移。平均位置位移是累积的，随着连续的音爆而增加。当作为频率的函数绘制时，即时偏移响应的幅度似乎呈现出三峰模式。在探头位置的特征频率（CF）处，这种位移偏移朝向SV，而在CF之上或之下的频率处，偏移相对较大，并且朝向ST。因此，基底膜的机械运动似乎包含侧向抑制的基础。然而，累积平均位置位移似乎在行波包络的顶端朝向ST达到峰值，并且似乎与一种共振相关，不是直接与基底膜运动的共振，而是与之耦合。同时在圆窗处测量的总和电位在探头位置的CF上方显示出一个调谐更宽的峰值。这似乎对应于机械偏置CF处的峰值。随着标本质量下降，振动位移响应的最佳频率降低到比原始CF低约半个八度。对音爆的不对称响应的三峰模式的峰值频率相应降低。三峰模式也变宽。在先前的实验中，基底膜已被强制响应低频偏置音而移动。对高频刺激的敏感性与偏置音同相变化。在这些早期实验和本实验中，缓慢运动的幅度处于相同的数量级。这强烈表明，向高频声刺激的累积向ST位移对同一高频区域的耳蜗敏感性构成了实质性的控制偏置。其效果将是降低CF高频侧神经放电率-强度函数的斜率。
