Akimov Alexander G, Egorova Marina A, Ehret Günter
Sechnov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
Institute of Neurobiology, University of Ulm, D-89069, Ulm, Germany.
Eur J Neurosci. 2017 Feb;45(3):440-459. doi: 10.1111/ejn.13488. Epub 2017 Jan 4.
Selectivity for processing of species-specific vocalizations and communication sounds has often been associated with the auditory cortex. The midbrain inferior colliculus, however, is the first center in the auditory pathways of mammals integrating acoustic information processed in separate nuclei and channels in the brainstem and, therefore, could significantly contribute to enhance the perception of species' communication sounds. Here, we used natural wriggling calls of mouse pups, which communicate need for maternal care to adult females, and further 15 synthesized sounds to test the hypothesis that neurons in the central nucleus of the inferior colliculus of adult females optimize their response rates for reproduction of the three main harmonics (formants) of wriggling calls. The results confirmed the hypothesis showing that average response rates, as recorded extracellularly from single units, were highest and spectral facilitation most effective for both onset and offset responses to the call and call models with three resolved frequencies according to critical bands in perception. In addition, the general on- and/or off-response enhancement in almost half the investigated 122 neurons favors not only perception of single calls but also of vocalization rhythm. In summary, our study provides strong evidence that critical-band resolved frequency components within a communication sound increase the probability of its perception by boosting the signal-to-noise ratio of neural response rates within the inferior colliculus for at least 20% (our criterion for facilitation). These mechanisms, including enhancement of rhythm coding, are generally favorable to processing of other animal and human vocalizations, including formants of speech sounds.
对物种特异性发声和交流声音进行处理的选择性通常与听觉皮层有关。然而，中脑下丘是哺乳动物听觉通路中的第一个中心，它整合了在脑干中不同核团和通道中处理的声学信息，因此可能对增强对物种交流声音的感知有显著贡献。在这里，我们使用了幼鼠的自然蠕动叫声，这种叫声向成年雌性传达对母性关怀的需求，并且还使用了另外15种合成声音来测试以下假设：成年雌性下丘中央核中的神经元会优化其反应率，以重现蠕动叫声的三个主要谐波（共振峰）。结果证实了这一假设，表明从单个神经元胞外记录到的平均反应率最高，并且对于根据感知中的临界带宽具有三个分辨频率的叫声和叫声模型，其起始和终止反应的频谱促进最为有效。此外，在被研究的122个神经元中，几乎一半的神经元普遍存在的开启和/或关闭反应增强不仅有利于对单个叫声的感知，也有利于对发声节奏的感知。总之，我们的研究提供了强有力的证据，即交流声音中临界带宽分辨的频率成分通过将下丘内神经反应率的信噪比提高至少20%（我们的促进标准），增加了其被感知的概率。这些机制，包括节奏编码的增强，通常有利于处理其他动物和人类的发声，包括语音的共振峰。
