Andoni Sari, Li Na, Pollak George D
Section of Neurobiology, Institute for Neuroscience, and Center for Perceptual Systems, The University of Texas at Austin, Austin, Texas 78712, USA.
J Neurosci. 2007 May 2;27(18):4882-93. doi: 10.1523/JNEUROSCI.4342-06.2007.
Frequency modulations are a prominent feature of animal vocalizations and human speech. Here we investigated how neurons in the inferior colliculus (IC) of Mexican free-tailed bats respond to the frequency-modulated (FM) direction and velocity of complex signals by extracting their spectrotemporal receptive fields (STRFs) using a family of upward- and downward-moving ripple stimuli. STRFs were obtained in more than half of the cells that were sampled. To verify the validity of each STRF, we compared their features both with tone-evoked responses and by convolving the STRF with several conspecific calls. We show that responses to tones are in close agreement with the STRF and that the responses predicted by convolutions compare favorably with responses evoked by those calls. The high predictability showed that the STRF captured most of the excitatory and inhibitory properties of IC cells. Most neurons were selective for the direction and velocity of spectral motion with a majority favoring the downward FM direction, and most had spectrum-time inseparability that correlated with their direction selectivity. Furthermore, blocking inhibition significantly reduced the directional selectivity of these neurons, suggesting that inhibition shapes FM direction selectivity in the IC. Finally, we decomposed the natural calls into their ripple components and show that most species-specific calls have downward-sweeping FM components with sweep velocities that correspond with the preferred sweep velocities of IC neurons. This close quantitative correspondence among features of signals and responses suggests that IC cells are tuned by inhibition to respond optimally to spectral motion cues present in their conspecific vocalizations.
频率调制是动物发声和人类语言的一个显著特征。在这里，我们研究了墨西哥无尾蝠下丘（IC）中的神经元如何通过使用一系列向上和向下移动的波纹刺激来提取它们的频谱时间感受野（STRF），从而对复杂信号的频率调制（FM）方向和速度做出反应。在超过一半的采样细胞中获得了STRF。为了验证每个STRF的有效性，我们将它们的特征与音调诱发反应进行了比较，并通过将STRF与几个同种叫声进行卷积来进行比较。我们表明，对音调的反应与STRF密切一致，并且卷积预测的反应与那些叫声诱发的反应相比具有优势。高预测性表明STRF捕捉到了IC细胞的大部分兴奋性和抑制性特性。大多数神经元对频谱运动的方向和速度具有选择性，大多数倾向于向下的FM方向，并且大多数具有频谱 - 时间不可分离性，这与它们的方向选择性相关。此外，阻断抑制作用显著降低了这些神经元的方向选择性，表明抑制作用塑造了IC中的FM方向选择性。最后，我们将自然叫声分解为它们的波纹成分，并表明大多数物种特异性叫声具有向下扫描的FM成分，其扫描速度与IC神经元的首选扫描速度相对应。信号和反应特征之间这种紧密的定量对应表明，IC细胞通过抑制作用进行调谐，以对同种发声中存在的频谱运动线索做出最佳反应。
