Tuning of SFOAEs Evoked by Low-Frequency Tones Is Not Compatible with Localized Emission Generation
Tuning of SFOAEs Evoked by Low-Frequency Tones Is Not Compatible with Localized Emission Generation
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DOI：
10.1007/s10162-015-0513-0
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发表时间：
2015-06-01
影响因子：
2.4
通讯作者：
Siegel, Jonathan H.
中科院分区：
文献类型：
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作者：
Charaziak, Karolina K.;Siegel, Jonathan H.
刺激频率耳声发射 (SFOAE) 似乎非常适合评估频率选择性，因为至少在理论上，它们起源于诱发音调特征位置附近的耳蜗受限区域。为了支持这一观点，我们之前发现龙猫中频率高于 3 kHz 的 SFOAE 抑制调谐曲线 (SF-STC) 与频率选择性控制措施（复合动作电位抑制调谐曲线 (CAP-STC)）之间具有良好的一致性。然而，对于较低频率，SF-STC 的宽度是 CAP-STC 的五倍以上，并且表现出更多的高通而不是窄带通滤波器特性。在这里，我们测试了这样的假设：低频 SF-STC 的广泛调谐是因为发射源自耳蜗的广泛区域，从基底延伸到诱发音调的特征位置。我们通过使用高频干扰音（IT；75 dB 声压级 (SPL) 下的 4.2、6.2 或 9.2 kHz）进行预抑制，或者通过在高频下诱发声损伤（暴露于 110-115 dB SPL 下的 8、5 和最后的 3 kHz 音调）来消除假设的位于基底的 SFOAE 源的贡献。测量 1kHz SF-STC 和 CAP-STC 的基线、IT 存在以及麻醉龙猫的声损伤情况。 IT 和声损伤对 SF-STC 的影响几乎无法区分。随着 IT 频率降低以及随后暴露于低频音调，SF-STC 逐渐从宽高通形状变为窄带通形状。这两个结果都与“基本来源”假设一致。相比之下，CAP-STC 没有因任何操作而改变，这表明 IT 和声损伤都没有影响 1-kHz 特征位置。因此，与 CAP 不同，SFOAE 不能被视为低频耳蜗功能的特定地点测量，至少对于龙猫来说是这样。
Stimulus-frequency otoacoustic emissions (SFOAEs) appear to be well suited for assessing frequency selectivity because, at least on theoretical grounds, they originate over a restricted region of the cochlea near the characteristic place of the evoking tone. In support of this view, we previously found good agreement between SFOAE suppression tuning curves (SF-STCs) and a control measure of frequency selectivity (compound action potential suppression tuning curves (CAP-STC)) for frequencies above 3 kHz in chinchillas. For lower frequencies, however, SF-STCs and were over five times broader than the CAP-STCs and demonstrated more high-pass rather than narrow band-pass filter characteristics. Here, we test the hypothesis that the broad tuning of low-frequency SF-STCs is because emissions originate over a broad region of the cochlea extending basal to the characteristic place of the evoking tone. We removed contributions of the hypothesized basally located SFOAE sources by either pre-suppressing them with a high-frequency interference tone (IT; 4.2, 6.2, or 9.2 kHz at 75 dB sound pressure level (SPL)) or by inducing acoustic trauma at high frequencies (exposures to 8, 5, and lastly 3-kHz tones at 110-115 dB SPL). The 1-kHz SF-STCs and CAP-STCs were measured for baseline, IT present and following the acoustic trauma conditions in anesthetized chinchillas. The IT and acoustic trauma affected SF-STCs in an almost indistinguishable way. The SF-STCs changed progressively from a broad high-pass to narrow band-pass shape as the frequency of the IT was lowered and for subsequent exposures to lower-frequency tones. Both results were in agreement with the "basal sources" hypothesis. In contrast, CAP-STCs were not changed by either manipulation, indicating that neither the IT nor acoustic trauma affected the 1-kHz characteristic place. Thus, unlike CAPs, SFOAEs cannot be considered as a place-specific measure of cochlear function at low frequencies, at least in chinchillas.