Bergevin Christopher, Whiley Rebecca E, Wit Hero, Manley Geoffrey A, van Dijk Pim
Department of Physics & Astronomy, York University, Toronto, ON, Canada.
Department of Biology, York University, Toronto, ON, Canada.
Biophys J. 2025 Apr 15;124(8):1208-1225. doi: 10.1016/j.bpj.2025.02.023. Epub 2025 Mar 3.
As a sound pressure detector that uses energy to boost both its sensitivity and selectivity, the inner ear is an active nonequilibrium system. The collective processes of the inner ear that give rise to this exquisite functionality remain poorly understood. One manifestation of the active ear across the animal kingdom is the presence of spontaneous otoacoustic emission (SOAE), idiosyncratic arrays of spectral peaks that can be measured using a sensitive microphone in the ear canal. Current SOAE models attempt to explain how multiple peaks arise, and generally assume a spatially distributed tonotopic system. However, the nature of the generators, their coupling, and the role of noise (e.g., Brownian motion) are hotly debated, especially given the inner ear morphological diversity across vertebrates. One means of probing these facets of emission generation is studying fluctuations in SOAE peak properties, which produce amplitude and frequency modulations (AM and FM, respectively). These properties are likely related to the presence of noise affecting active cellular generation elements, and the coupling between generators. To better biophysically constrain models, this study characterizes the fluctuations in filtered SOAE peak waveforms, focusing on interrelations within and across peaks. A systematic approach is taken, examining three species that exhibit disparate inner ear morphologies: humans, barn owls, and green anole lizards. To varying degrees across all three groups, SOAE peaks have intrapeak (IrP) and interpeak (IPP) correlations indicative of interactions between generative elements. Activity from anole lizards, whose auditory sensory organ is relatively much smaller than that of humans or barn owls, showed a much higher incidence of nearest-neighbor IPP correlations. We propose that these data reveal characteristics of SOAE cellular generators acting cooperatively, allowing the ear to function as an optimized detector.
作为一种利用能量来提高其灵敏度和选择性的声压探测器，内耳是一个活跃的非平衡系统。内耳产生这种精妙功能的集体过程仍知之甚少。在动物界，活跃耳朵的一个表现是自发性耳声发射（SOAE）的存在，这是一种可以通过耳道内的灵敏麦克风测量到的独特频谱峰值阵列。当前的SOAE模型试图解释多个峰值是如何产生的，并且通常假设存在一个空间分布的音调定位系统。然而，发生器的性质、它们的耦合以及噪声（例如布朗运动）的作用存在激烈争论，特别是考虑到脊椎动物内耳形态的多样性。探究发射产生这些方面的一种方法是研究SOAE峰值特性的波动，这些波动分别产生幅度调制和频率调制（AM和FM）。这些特性可能与影响活跃细胞生成元件的噪声的存在以及发生器之间的耦合有关。为了更好地从生物物理角度限制模型，本研究对滤波后的SOAE峰值波形的波动进行了表征，重点关注峰值内部和峰值之间的相互关系。我们采用了一种系统的方法，研究了三种具有不同内耳形态的物种：人类、仓鸮和绿安乐蜥。在所有这三组中，SOAE峰值在不同程度上具有峰内（IrP）和峰间（IPP）相关性，这表明生成元件之间存在相互作用。绿安乐蜥的听觉感觉器官相对比人类或仓鸮的小得多，其活动显示出最近邻IPP相关性的发生率要高得多。我们认为，这些数据揭示了SOAE细胞发生器协同作用的特征，使耳朵能够作为一个优化的探测器发挥作用。
