Nam Hui, Guinan John J
Eaton-Peabody Lab, Mass Eye and Ear Infirmary, 243 Charles St., Boston MA 02114, USA; Harvard-MIT HST Speech and Hearing Bioscience and Technology Program, Cambridge MA, USA.
Eaton-Peabody Lab, Mass Eye and Ear Infirmary, 243 Charles St., Boston MA 02114, USA; Harvard-MIT HST Speech and Hearing Bioscience and Technology Program, Cambridge MA, USA; Harvard Medical School, Boston MA, USA.
Hear Res. 2016 Nov;341:66-78. doi: 10.1016/j.heares.2016.08.007. Epub 2016 Aug 29.
We used low-frequency "bias" tones (BT's) to explore whether click and tone responses are affected in the same way by cochlear active processes. In nonlinear systems the responses to clicks are not always simply related to the responses to tones. Cochlear amplifier gain depends on the incremental slope of the outer-hair-cell (OHC) stereocilia mechano-electric transduction (MET) function. BTs transiently change the operating-point of OHC MET channels and can suppress cochlear-amplifier gain by pushing OHC METs into low-slope saturation regions. BT effects on single auditory-nerve (AN) fibers have been studied on tone responses but not on click responses. We recorded from AN fibers in anesthetized cats and compared tone and click responses using 50 Hz BTs at 70-120 dB SPL to manipulate OHC stereocilia position. BTs can also excite and thereby obscure the BT suppression. We measured AN-fiber response synchrony to BTs alone so that we could exclude suppression measurements when the BT synchrony might obscure the suppression. BT suppression of low-level tone and click responses followed the traditional pattern of twice-a-BT-cycle suppression with more suppression at one phase than the other. The major suppression phases of most fibers were tightly grouped with little difference between click and tone suppressions, which is consistent with low-level click and tone responses being amplified in the same way. The data are also consistent with the operating point of the OHC MET function varying smoothly from symmetric in the base to offset in the apex, and, in contrast, with the IHC MET function being offset throughout the cochlea. As previously reported, bias-tones presented alone excited AN fibers at one or more phases, a phenomena termed "peak splitting" with most BT excitation phases ∼¼ cycle before or after the major suppression phase. We explain peak splitting as being due to distortion in multiple fluid drives to inner-hair-cell stereocilia.
我们使用低频“偏置”音（BT）来探究耳蜗主动过程对咔嗒声和纯音反应的影响方式是否相同。在非线性系统中，对咔嗒声的反应并不总是与对纯音的反应简单相关。耳蜗放大器增益取决于外毛细胞（OHC）静纤毛机械电转导（MET）功能的增量斜率。BT会短暂改变OHC MET通道的工作点，并通过将OHC METs推至低斜率饱和区域来抑制耳蜗放大器增益。关于BT对单根听神经（AN）纤维的影响，已有研究针对纯音反应，但未涉及咔嗒声反应。我们在麻醉猫的AN纤维上进行记录，并使用70 - 120 dB SPL的50 Hz BT来操纵OHC静纤毛位置，比较纯音和咔嗒声反应。BT也会产生兴奋作用，从而掩盖BT抑制效应。我们单独测量了AN纤维对BT的反应同步性，以便在BT同步性可能掩盖抑制效应时排除抑制测量。BT对低强度纯音和咔嗒声反应的抑制遵循传统模式，即每两个BT周期抑制一次，其中一个相位的抑制比另一个相位更强。大多数纤维的主要抑制相位紧密聚集，咔嗒声和纯音抑制之间差异不大，这与低强度咔嗒声和纯音反应以相同方式放大一致。数据还与OHC MET功能的工作点从基部的对称状态到顶部的偏移状态平滑变化一致，相反，与内毛细胞（IHC）MET功能在整个耳蜗中都处于偏移状态一致。如先前报道，单独呈现的偏置音会在一个或多个相位兴奋AN纤维，这种现象称为“峰值分裂”，大多数BT兴奋相位在主要抑制相位之前或之后约¼周期。我们将峰值分裂解释为是由于多个液体驱动内毛细胞静纤毛时产生的失真所致。
