Human Medial Olivocochlear Reflex: Effects as Functions of Contralateral, Ipsilateral, and Bilateral Elicitor Bandwidths
Human Medial Olivocochlear Reflex: Effects as Functions of Contralateral, Ipsilateral, and Bilateral Elicitor Bandwidths
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DOI：
10.1007/s10162-009-0163-1
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发表时间：
2009-09-01
影响因子：
2.4
通讯作者：
Guinan, John J., Jr.
中科院分区：
文献类型：
--
作者：
Lilaonitkul, Watjana;Guinan, John J., Jr.
动物研究表明，内侧橄榄耳蜗（MOC）传出反射提供了抑制耳蜗放大的急剧调谐的频率特异性反馈。为了确定MOC激活是否确实是窄带的，我们测量了由60 dB声压级（SPL）对侧，同侧和双侧噪声频带引起的人类MOC效应，作为1/2至6.7倍频程噪声带宽的函数。MOC效应通过刺激频率耳声发射从40 dB SPL探测音接近0.5、1和4 kHz的变化来量化。在第二个实验中，噪声带的中心低于探测频率2个倍频程，接近1和4 kHz。在所有情况下，MOC效应随着激发子带宽的增加而增加，该效应在约4个倍频程处饱和。一般来说，MOC效应随着探头频率的降低而增加，与基于耳蜗中MOC神经支配密度的预期相反。双向诱导效应总是最大的。同侧/对侧效应的比率取决于激发子带宽;该比率对于窄带探针为中心的激发子是大的，对于宽带激发子是近似统一的。在另一个实验中，从相邻半倍频程噪声带的MOC效应的测量值计算增加激发子带宽的MOC效应。预测的带宽函数与测量的对侧激发子的带宽函数一致，但高估了同侧和双侧激发子。总的来说，结果表明：（1）MOC反射整合了来自几乎整个耳蜗长度的激励，（2）随着激发子带宽的增加，来自新刺激的耳蜗区域的激励超过了在激发子频带中心的频率处的减少的激励，以及（3）对侧、同侧和双侧激发子在大多数耳蜗上显示出MOC反射空间总和，但同侧空间总和比对侧的相加性小。
Animal studies have led to the view that the acoustic medial olivocochlear (MOC) efferent reflex provides sharply tuned frequency-specific feedback that inhibits cochlear amplification. To determine if MOC activation is indeed narrow band, we measured the MOC effects in humans elicited by 60-dB sound pressure level (SPL) contralateral, ipsilateral, and bilateral noise bands as a function of noise bandwidth from 1/2 to 6.7 octaves. MOC effects were quantified by the change in stimulus frequency otoacoustic emissions from 40 dB SPL probe tones near 0.5, 1, and 4 kHz. In a second experiment, the noise bands were centered 2 octaves below probe frequencies near 1 and 4 kHz. In all cases, the MOC effects increased as elicitor bandwidth increased, with the effect saturating at about 4 octaves. Generally, the MOC effects increased as the probe frequency decreased, opposite expectations based on MOC innervation density in the cochlea. Bilateral-elicitor effects were always the largest. The ratio of ipsilateral/contralateral effects depended on elicitor bandwidth; the ratio was large for narrow-band probe-centered elicitors and approximately unity for wide-band elicitors. In another experiment, the MOC effects from increasing elicitor bandwidths were calculated from measurements of the MOC effects from adjacent half-octave noise bands. The predicted bandwidth function agreed well with the measured bandwidth function for contralateral elicitors, but overestimated it for ipsilateral and bilateral elicitors. Overall, the results indicate that (1) the MOC reflexes integrate excitation from almost the entire cochlear length, (2) as elicitor bandwidth is increased, the excitation from newly stimulated cochlear regions more than overcomes the reduced excitation at frequencies in the center of the elicitor band, and (3) contralateral, ipsilateral, and bilateral elicitors show MOC reflex spatial summation over most of the cochlea, but ipsilateral spatial summation is less additive than contralateral.