Altoè Alessandro, Shera Christopher A
Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, USA.
AIP Conf Proc. 2024 Feb 27;3062(1). doi: 10.1063/5.0193604.
According to the dominant view, the mammalian cochlea spatially amplifies signals by actively pumping energy into the traveling wave. That is, signals are amplified as they propagate through a region where the medium's resistance is effectively negative. While signal amplification has been extensively studied in active cochlear models, the same cannot be said for amplification of internal noise. According to transmission-line theory, signals are amplified more than internal noise in regions where the net resistance is negative. Here we generalize this finding by showing that a distributed system composed of cascaded "noisy" amplifiers boosts signals more rapidly than the internal noise; the larger the amplifier gain, the larger the signal-to-noise ratio (SNR) of the amplified signal. We further show that this mechanism operates in existing active cochlear models: the cochlear amplifier increases the SNR of cochlear responses, and thus enhances cochlear sensitivity. When considering also that the cochlear amplifier narrows the bandwidth of the "cochlear filters", activation of the cochlear amplifiers dramatically increases the SNR (by about one order of magnitude in our simulations) from the tail to the peak of the traveling wave. We further demonstrate that the tapered ear-horn-like cochlear geometry significantly improves the SNR of basilar-membrane responses.
根据主流观点，哺乳动物的耳蜗通过向行波中主动注入能量在空间上放大信号。也就是说，信号在通过介质阻力实际上为负的区域传播时会被放大。虽然在有源耳蜗模型中对信号放大进行了广泛研究，但对于内部噪声的放大情况却并非如此。根据传输线理论，在净电阻为负的区域，信号比内部噪声放大得更多。在此，我们通过表明由级联“有噪声”放大器组成的分布式系统比内部噪声更快地增强信号来推广这一发现；放大器增益越大，放大信号的信噪比（SNR）就越大。我们进一步表明，这种机制在现有的有源耳蜗模型中起作用：耳蜗放大器增加了耳蜗反应的信噪比，从而提高了耳蜗的灵敏度。当还考虑到耳蜗放大器会缩小“耳蜗滤波器”的带宽时，耳蜗放大器的激活会使从行波的尾部到峰值的信噪比显著增加（在我们的模拟中增加约一个数量级）。我们进一步证明，呈喇叭状逐渐变细的耳蜗几何形状显著提高了基底膜反应的信噪比。
