Based on single-unit recordings of modulation transfer functions (MTFs) in the inferior colliculus (IC) and the medial geniculate body (MGB) of the unanesthetized rabbit, we identified two opposing populationsband-enhanced (BE) and band-suppressed (BS) neurons. In response to amplitude-modulated (AM) sounds, firing rates of BE and BS neurons were enhanced and suppressed, respectively, relative to their responses to an unmodulated noise with a one-octave bandwidth. We also identified a third population, designated hybrid neurons, whose firing rates were enhanced by some modulation frequencies and suppressed by others. Our finding suggests that perception of AM may be based on the co-occurrence of enhancement and suppression of responses of the opposing populations of neurons. Since AM carries an important part of the content of speech, progress in understanding auditory processing of AM sounds should lead to progress in understanding speech perception. Each of the BE, BS and hybrid types of MTFs comprised approximately 1/3 of the total sample. Modulation envelopes having short duty cycles of 20 to 50% and raised-sine envelopes accentuated the degree of enhancement and suppression and sharpened tuning of the MTFs. With sinusoidal envelopes, peak modulation frequencies were centered around 32-64 Hz among IC BE neurons, whereas the MGB peak frequencies skewed towards lower frequencies, with a median of 16 Hz. We also tested an auditory-brainstem model and found that a simple circuit containing fast excitatory synapses and slow inhibitory synapses was able to reproduce salient features of the BE and BS type MTFs of IC neurons.

中文翻译：

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幅度调制传递函数揭示了下丘和内侧膝状体内的相反群体。


基于未麻醉兔子的下丘 (IC) 和内侧膝状体 (MGB) 的调制传递函数 (MTF) 的单单元记录，我们确定了两个相反的群体带增强 (BE) 和带抑制 (BS)神经元。相对于对一倍频程带宽的未调制噪声的反应，BE 和 BS 神经元对调幅 (AM) 声音的反应分别增强和抑制。我们还确定了第三个群体，称为混合神经元，其放电率因某些调制频率而增强，而被其他频率抑制。我们的发现表明，对 AM 的感知可能基于相反神经元群反应的增强和抑制的同时发生。由于 AM 承载着语音内容的重要部分，因此理解 AM 声音的听觉处理的进展应该会导致理解语音感知的进展。 BE、BS 和混合类型的 MTF 均约占总样本的 1/3。具有 20% 至 50% 的短占空比的调制包络和升高的正弦包络强调了 MTF 的增强和抑制以及锐化调谐的程度。对于正弦包络，IC BE 神经元的峰值调制频率集中在 32-64 Hz 左右，而 MGB 峰值频率偏向较低频率，中位数为 16 Hz。我们还测试了听觉脑干模型，发现包含快速兴奋性突触和慢速抑制性突触的简单电路能够重现 IC 神经元的 BE 和 BS 型 MTF 的显着特征。