Sohmer Haim, Freeman Sharon, Perez Ronen
Department of Physiology, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel.
Hear Res. 2004 Jan;187(1-2):105-10. doi: 10.1016/s0378-5955(03)00335-6.
Auditory stimulation can, under certain circumstances, activate the vestibular end organs and this is facilitated by fenestration of a semicircular canal (SCC). Several fenestrated profoundly deaf patients reported improvements in their bone- (BC) but not air-conducted (AC) thresholds. Bone conduction auditory thresholds have been reported to be better than normal in several patients with thinning or absence of bone over a SCC (dehiscence). This phenomenon was carefully studied in the fat sand rat (Psammomys obesus) by recording auditory brainstem evoked responses to BC and AC auditory stimulation, before and after SCC fenestration. Fenestration would be expected to decrease the pressure difference across the cochlear partition, causing a reduction in the amplitude of the classical base to apex input traveling wave, and should therefore lead to an elevation in AC and BC thresholds. Instead, BC thresholds decreased (i.e. improved) following fenestration (by 7.0+/-4.2 dB; P<0.005), while AC thresholds did not change. Thus the cochlea becomes more sensitive to BC, but not AC, stimulation in the presence of a SCC fenestration. This may be due to the removal by the fenestration of a factor impeding BC cochlear responses, or by the addition of a facilitating factor. The result that the SCC fenestration did not affect AC threshold provides support for the concept that at low intensities the outer hair cells are directly activated by components of the fluid pressures surrounding them, which alternate at audio-frequencies. These cochlear fluid audio-frequency pressures are induced by stapes footplate movement and not by a base to apex input traveling wave. The audio-frequency pressures would not be affected by SCC fenestration. The outer hair cell motility thus induced somehow excites the inner hair cells and the auditory nerve fibers. At low intensities the outer hair cell motility causes localized displacement at the appropriate position on the basilar membrane.
在某些情况下，听觉刺激可激活前庭终器，而半规管开窗可促进这种激活。一些接受了开窗手术的极重度聋患者报告称，其骨导（BC）阈值有所改善，但气导（AC）阈值未变。据报道，在一些半规管上方骨质变薄或缺失（骨裂）的患者中，其骨导听觉阈值优于正常水平。通过记录在半规管开窗前后对骨导和气导听觉刺激的听觉脑干诱发电位，在肥沙鼠（肥尾沙鼠）身上对这一现象进行了仔细研究。开窗预计会减小跨蜗管隔板的压力差，导致经典的从基底到蜗顶的输入行波幅度减小，因此应会导致气导和骨导阈值升高。然而，开窗后骨导阈值降低（即改善）（降低了7.0±4.2 dB；P<0.005），而气导阈值未改变。因此，在存在半规管开窗的情况下，耳蜗对骨导刺激变得更加敏感，但对气导刺激并非如此。这可能是由于开窗去除了阻碍骨导耳蜗反应的因素，或者是由于添加了促进因素。半规管开窗不影响气导阈值这一结果支持了以下概念：在低强度时，外毛细胞由其周围流体压力的成分直接激活，这些压力在音频频率下交替变化。这些耳蜗流体音频压力是由镫骨足板运动引起的，而不是由从基底到蜗顶的输入行波引起的。音频压力不会受到半规管开窗的影响。由此诱导的外毛细胞运动以某种方式激发内毛细胞和听觉神经纤维。在低强度时，外毛细胞运动在基底膜上的适当位置引起局部位移。
