EFFECTS OF ELECTRICAL-STIMULATION OF EFFERENT OLIVOCOCHLEAR NEURONS ON CAT AUDITORY-NERVE FIBERS .3. TUNING CURVES AND THRESHOLDS AT CF
EFFECTS OF ELECTRICAL-STIMULATION OF EFFERENT OLIVOCOCHLEAR NEURONS ON CAT AUDITORY-NERVE FIBERS .3. TUNING CURVES AND THRESHOLDS AT CF
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DOI：
10.1016/0378-5955(88)90075-5
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发表时间：
1988-12-01
期刊：
影响因子：
2.8
通讯作者：
GIFFORD, ML
中科院分区：
文献类型：
--
作者：
GUINAN, JJ;GIFFORD, ML
为了研究传出活动的影响，橄榄耳蜗传出刺激与电极在第四脑室交叉橄榄耳蜗束的交叉（中线OCB刺激）或与电极在脑干起源的内侧传出（MOC刺激）。在传出刺激存在或不存在的情况下，从迷走神经纤维获得转向曲线或类似的阈值测量。传出刺激提高了在特征频率（CF）的音调的纤维的阈值的量，其变化与自发率（SR）的神经纤维。平均而言，高SR纤维的阈值偏移最小，低SR纤维的阈值偏移最大。高SR和中SR纤维的阈值位移分布作为CF的函数在3-8 kHz的CF处达到峰值，但低SR纤维的阈值位移分布在更高的CF处达到峰值。在高SR或中SR组中，具有最低阈值的纤维具有最大的阈值偏移。传出刺激降低了大多数纤维的调谐曲线的Q20（即它使调谐曲线变宽），但增加了一些纤维的Q20与CF低于2 kHz。对于CFs高于4 kHz的纤维，传出刺激将转向曲线尾部移动到平均约1 dB的较高声级。中线OCB刺激或MOC刺激的效应的定性模式相似。与外毛细胞上MOC末梢的分布相比，高SR阈值偏移与CF的分布似乎在耳蜗中被顶向移位。这可以从传出活动抑制基底膜运动和影响激活的传出突触处和顶端的区域来理解。为了解释低SR阈值变化，似乎需要传出活动抑制反应的另一种方式。这些数据与内侧传出神经的功能之一是提高听觉神经纤维的阈值，从而调整听觉系统的有效范围是一致的。
In order to study the effects of efferent activity, olivocochlear efferents were stimulated with an electrode in the fourth ventricle at the decussation of the crossed olivocochlear bundle (midline-OCB stimulation) or with an electrode at the brainstem origin of medial efferents (MOC stimulation). Turning curves, or similar measures of threshold, were obtained from auditory-nerve fibers in the presence or absence of efferent stimulation. Efferent stimulation raised the thresholds of fibers for tones at the characteristic frequency (CF) by an amount which varied with the spontaneous rate (SR) of the auditory-nerve fiber. On the average, high-SR fibers had the smallest threshold shifts, and low-SR fibers had the largest threshold shifts. The distribution of threshold shifts as a function of CF peaked at CFs of 3-8 kHz for high-SR and medium-SR fibers but appeared to peak at higher CFs for low-SR fibers. Within the high-SR or medium-SR groups, the fibers with the lowest thresholds had the largest threshold shifts. Efferent stimulation decreased the Q20 of the tuning curves from most fibers (i.e. it made the tuning curves wider), but increased the Q20 from some fibers with CFs below 2 kHz. For fibers with CFs above 4 kHz, efferent stimulation shifted the turning-curve tails to higher sound levels by about 1 dB on the average. The qualitative patterns of the effects due to midline-OCB stimulation or to MOC stimulation were similar. The distribution of high-SR threshold shifts vs. CF appears to be displaced apically in the cochlea compared to the distribution of MOC endings on outer hair cells. This can be understood in terms of efferent activity depressing basilar membrane motion and affecting regions at, and apical to, the activated efferent synapses. To explain the low-SR threshold shifts, an additional way in which efferent activity inhibits responses appears to be required. The data are consistent with one function of the medial efferents being to raise the thresholds of auditory-nerve fibers and thereby adjust the effective range of the auditory system.