Nuttall A L, Zheng J, Ren T, de Boer E
Oregon Hearing Research Center, Department of Otolaryngology/Head and Neck Surgery, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, NRC04, Portland, OR 97201-3098, USA.
Hear Res. 2001 Feb;152(1-2):77-89. doi: 10.1016/s0378-5955(00)00238-0.
Stimulation of the cochlea with sinusoidal current results in the production of an otoacoustic emission at the primary frequency of the stimulus current. In this study we test the hypothesis that the wide frequency response from round window (RW) stimulation is due to the involvement of a relatively large spatial segment of the organ of Corti. Tonotopically organized group delays would be evident from perilymphatic electrode locations that restrict the spatial extent of hair cell stimulation. Monopolar and bipolar-paired stimulus electrodes were placed in perilymphatic areas of the first or third cochlear turns and the electrically evoked otoacoustic emissions (EEOAE) produced by these electrodes were compared to that from the RW monopolar electrode in the anesthetized guinea pig. Current stimuli of 35 microA RMS were swept across the frequency range between 60 Hz and 100 kHz. The EEOAE was measured using a microphone coupled to the ear canal. It was found that the bandwidth of EEOAEs from RW stimulation extended to at least 40 kHz and was a relatively insensitive to electrode location on the RW. The group delay of the EEOAE from stimulation at the RW membrane (corrected to stapes motion) was about 53 micros. First and third turn stimulations from electrode placements in perilymph near the bony wall of cochlea yielded narrower band EEOAE magnitude spectra but which had the same short group delays as for RW stimulation. A confined current (from a bipolar electrode pair) applied close to the basilar membrane (BM) in the first turn produced the narrowest frequency-band magnitude emissions and a mean corrected group delay of 176 micros for a location approximately 3 mm from the high frequency end of the BM (corresponding to about the 18 kHz best frequency location). Bipolar electrodes in the third turn scala tympani produced low pass EEOAE magnitude functions with corrected group delays ranging between approximately 0.3 and 1 ms. The average phase slopes did not change with altered cochlear sensitivity and postmortem. These data indicate that the EEOAE from RW stimulation is the summed response from a wide-tonotopic distribution of outer hair cells. A preliminary model study indicates that short time delayed emissions are the result of a large spatial distribution of current applied to perilymphatic locations possibly giving rise to "wave-fixed" emissions.
用正弦电流刺激耳蜗会在刺激电流的基频处产生耳声发射。在本研究中，我们检验了这样一个假设，即圆窗（RW）刺激产生的宽频率响应是由于柯蒂氏器相对较大的空间段参与所致。从限制毛细胞刺激空间范围的外淋巴电极位置可以明显看出频率组织化的群延迟。将单极和双极配对刺激电极置于第一或第三耳蜗转的外淋巴区域，并将这些电极产生的电诱发耳声发射（EEOAE）与麻醉豚鼠中RW单极电极产生的EEOAE进行比较。35微安均方根值的电流刺激在60赫兹至100千赫兹的频率范围内扫描。使用与耳道耦合的麦克风测量EEOAE。结果发现，RW刺激产生的EEOAE带宽扩展到至少40千赫兹，并且对RW上的电极位置相对不敏感。RW膜刺激产生的EEOAE的群延迟（校正为镫骨运动）约为53微秒。在靠近耳蜗骨壁的外淋巴中放置电极进行的第一转和第三转刺激产生了带宽较窄的EEOAE幅度谱，但与RW刺激具有相同的短群延迟。在第一转靠近基底膜（BM）处施加的受限电流（来自双极电极对）产生了最窄的频带幅度发射，对于距BM高频端约3毫米的位置（对应于约18千赫兹的最佳频率位置），平均校正群延迟为176微秒。第三转鼓阶中的双极电极产生低通EEOAE幅度函数，校正群延迟在约0.3至1毫秒之间。平均相位斜率不会随着耳蜗敏感性的改变和死后情况而变化。这些数据表明，RW刺激产生的EEOAE是外毛细胞广泛频率组织分布的总和响应。一项初步模型研究表明，短时间延迟发射是施加到外淋巴位置的电流大空间分布的结果，可能产生“波固定”发射。
