Department of Neurophysiology, JW Goethe-Universität Frankfurt, Neuroscience Center, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany.
Hear Res. 2010 Sep 1;268(1-2):184-93. doi: 10.1016/j.heares.2010.05.021. Epub 2010 Jun 4.
Accumulating evidence indicates that mammalian cochlear frequency-position maps (location of maximum vibration of the basilar membrane as a function of frequency) depend on the physiological condition of the inner ear. Cochlear damage desensitizes the ear, after the damage the original location of maximum vibration is tuned to a lower sound frequency. This suggests that frequency-position maps, derived from such desensitized ears, are shifted to lower frequencies, corresponding to a shift of the basilar membrane vibration pattern towards the base for a given stimulus frequency. To test this hypothesis, we re-mapped the cochlear frequency-position map in the chinchilla. We collected frequency-position data from chinchillas in normal physiological condition ("physiological map") and compared these to data previously established from sound overexposed ears ("anatomical map"). The characteristic frequency (CF) of neurons in the cochlear nucleus was determined. Horse-radish peroxidase (HRP) or biocytin (BCT) were injected iontophoretically to trace auditory nerve fibers towards their innervation site in the organ of Corti. The relationship between distance from the base (d, percent) and frequency (f, kHz) was described best by a simple exponential function: d = 61.2 - 42.2 x log(f). The slope of the function was 2.55 mm/octave. Compared to the "anatomical map", the "physiological map" was shifted by about 0.3 octaves to higher frequencies corresponding to a shift of the basilar membrane vibration pattern of 0.8 mm towards the apex for a given stimulus frequency. Our findings affirm that frequency-position maps in the mammalian cochlea depend on the condition of the inner ear. Damage-induced desensitization in mammalian inner ears results in similar shifts of CF (about 0.5 octaves) but different shifts of the maximum of the vibration pattern towards the base at given frequencies, dependent on the mapping constant of the species, longer basilar membranes showing a larger basal shift. Furthermore, the results substantiate the notion that "crowding" at lower frequencies appears to be a specialization rather than a general feature.
越来越多的证据表明,哺乳动物耳蜗的频率-位置图(基底膜最大振动位置随频率的变化)取决于内耳的生理状态。耳蜗损伤使耳朵脱敏,损伤后最大振动的原始位置被调谐到较低的声音频率。这表明,从脱敏耳获得的频率-位置图会向低频移动,与基底膜振动模式向特定刺激频率的基底移动相对应。为了验证这一假设,我们在南美栗鼠中重新绘制了耳蜗的频率-位置图。我们从正常生理状态下的南美栗鼠(“生理图谱”)中收集了频率-位置数据,并将其与先前从过度暴露于声音的耳朵中获得的数据(“解剖图谱”)进行了比较。确定了耳蜗核神经元的特征频率(CF)。辣根过氧化物酶(HRP)或生物素(BCT)被离子注入以追踪听神经纤维向其在耳蜗中的支配部位。距离基底(d,%)和频率(f,kHz)之间的关系最好用简单的指数函数来描述:d = 61.2 - 42.2 x log(f)。函数的斜率为 2.55 mm/octave。与“解剖图谱”相比,“生理图谱”向高频移动了约 0.3 个倍频程,对应于给定刺激频率时基底膜振动模式向顶点移动 0.8mm。我们的发现证实了哺乳动物耳蜗中的频率-位置图取决于内耳的状况。哺乳动物内耳的损伤诱导脱敏导致 CF 发生类似的移动(约 0.5 个倍频程),但在给定频率下,振动模式的最大值向基底的移动不同,这取决于物种的映射常数,较长的基底膜显示出更大的基底移动。此外,结果证实了“在较低频率处的拥挤”似乎是一种专门化而不是普遍特征的观点。