It is generally assumed that frequency selectivity varies along the cochlea. For example, at the base of the cochlea, which is a region sensitive to high-frequency sounds, the best frequency of a cochlear location increases toward the most basal end, that is, near the stapes. Response phases also vary along cochlear locations. At any given frequency, there is a decrease in phase lag toward the stapes. This tonotopic arrangement in the cochlea was originally described by Georg von Békésy in a seminal series of experiments on human cadavers and has been confirmed in more recent works on live laboratory animals. Nonetheless, our knowledge of tonotopy at the apex of the cochlea remains incomplete in animals with low-frequency hearing, which is relevant to human speech. The results of our experiments on guinea pig, gerbil, and chinchilla cochleas, regardless of the sex of the animal, show that responses to sound differ at locations across the apex in a pattern consistent with previous studies of the base of the cochlea.

SIGNIFICANCE STATEMENT Tonotopy is an important property of the auditory system that has been shown to exist in many auditory centers. In fact, most auditory implants work on the assumption of its existence by assigning different frequencies to different stimulating electrodes based on their location. At the level of the basilar membrane in the cochlea, a tonotopic arrangement implies that high-frequency stimuli evoke largest displacements at the base, near the ossicles, and low-frequency sounds have their greatest effects at the apex. Although tonotopy has been confirmed at the base of the cochlea on live animals at the apex of the cochlea, however, it has been less studied. Here, we show that a tonotopic arrangement does exist at the apex of the cochlea.

通常假设频率选择性沿着耳蜗变化。例如，在耳蜗基部，即对高频声音敏感的区域，耳蜗位置的最佳频率朝最基端，即镫骨附近增加。响应阶段也随着耳蜗位置的不同而变化。在任何给定频率下，镫骨的相位滞后都会减少。耳蜗中的这种音调排列最初是由乔治·冯·贝凯西 (Georg von Békésy) 在一系列对人类尸体进行的开创性实验中描述的，并在最近的活体实验动物研究中得到证实。尽管如此，我们对低频听力动物耳蜗顶端音调的了解仍然不完整，而低频听力与人类言语相关。我们对豚鼠、沙鼠和龙猫耳蜗的实验结果表明，无论动物的性别如何，耳蜗顶端位置对声音的反应有所不同，其模式与之前对耳蜗基部的研究一致。

意义声明音调是听觉系统的一个重要特性，已被证明存在于许多听觉中枢中。事实上，大多数听觉植入物的工作原理都是基于其存在的假设，根据刺激电极的位置将不同的频率分配给不同的刺激电极。在耳蜗基底膜的水平上，音位排列意味着高频刺激在听小骨附近的基部引起最大的位移，而低频声音在心尖处产生最大的影响。尽管已经在活体动物的耳蜗顶部证实了耳蜗基部的音调，但对其的研究较少。在这里，我们表明耳蜗顶端确实存在音调排列。