Rate Representation of Tones in Noise in the Inferior Colliculus of Decerebrate Cats
Rate Representation of Tones in Noise in the Inferior Colliculus of Decerebrate Cats
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DOI：
10.1007/s101620010029
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发表时间：
2000-08
期刊：
影响因子：
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通讯作者：
R. Ramachandran;K. A. Davis;B. May
中科院分区：
文献类型：
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作者：
R. Ramachandran;K. A. Davis;B. May
去大脑猫下丘中央核（ICC）神经元对不同频率和声压级的声音呈现三种主要的反应模式。I型单位的频率响应图由最佳频率（BF：单位最敏感的频率）处的狭窄兴奋区和较高和较低频率处的周围抑制唯一定义。由于这种感受野组织，I型单位表现出强烈的兴奋性反应BF音，但只有微弱的宽带噪声（BBN）。这些响应特性预测，I型单元非常适合在存在背景噪声的情况下对窄带信号进行编码。为了检验这一假设，ICC单元类型的动态范围特性在安静条件下和在多个连续噪声水平下进行测量。正如在以前的研究中观察到的听神经和耳蜗核，I型单位显示向上的阈值偏移和放电率压缩的背景噪声，部分退化的动态范围特性的神经表示在高噪声水平。虽然ICC中的其他两种单位类型在阈值偏移和噪声压缩方面表现出类似的趋势，但它们编码听觉信号的能力在增加噪声水平时受到更严重的损害。当双耳掩蔽效应进行了模拟，只有I型单位表现出增强的空间分离的信号和掩蔽，这是与人类的知觉表现在独立的心理声学观察一致的表示。这些结果支持的解释，即I型单位在背景噪声中的窄带信号的听觉处理中发挥了重要作用，并建议在自由场听力条件下的信号检测的空间因素的生理基础。
Neurons in the central nucleus of the inferior colliculus (ICC) of decerebrate cats show three major response patterns when tones of different frequencies and sound-pressure levels (SPLs) are presented to the contralateral ear. The frequency response maps of type I units are uniquely defined by a narrow excitatory area at best frequency (BF: a unit's most sensitive frequency) and surrounding inhibition at higher and lower frequencies. As a result of this receptive field organization, type I units exhibit strong excitatory responses to BF tones but respond only weakly to broadband noise (BBN). These response characteristics predict that type I units are well suited to encode narrowband signals in the presence of background noise. To test this hypothesis, the dynamic range properties of ICC unit types were measured under quiet conditions and in multiple levels of continuous noise. As observed in previous studies of the auditory nerve and cochlear nucleus, type I units showed upward threshold shifts and discharge rate compression in background noise that partially degraded the dynamic range properties of neural representations at high noise levels. Although the other two unit types in the ICC showed similar trends in threshold shift and noise compression, their ability to encode auditory signals was compromised more severely in increasing noise levels. When binaural masking effects were simulated, only type I units showed an enhanced representation of spatially separated signals and maskers that was consistent with human perceptual performance in independent psychoacoustic observations. These results support the interpretation that type I units play an important role in the auditory processing of narrowband signals in background noise and suggest a physiological basis for spatial factors that govern signal detection under free-field listening conditions.