Department of Biology, Humboldt-Universität zu Berlin, Berlin, Germany.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2011 Jan;197(1):61-74. doi: 10.1007/s00359-010-0587-4. Epub 2010 Sep 24.
Using modulation transfer functions (MTF), we investigated how sound patterns are processed within the auditory pathway of grasshoppers. Spike rates of auditory receptors and primary-like local neurons did not depend on modulation frequencies while other local and ascending neurons had lowpass, bandpass or bandstop properties. Local neurons exhibited broader dynamic ranges of their rate MTF that extended to higher modulation frequencies than those of most ascending neurons. We found no indication that a filter bank for modulation frequencies may exist in grasshoppers as has been proposed for the auditory system of mammals. The filter properties of half of the neurons changed to an allpass type with a 50% reduction of modulation depths. Contrasting to reports for mammals, the sensitivity to small modulation depths was not enhanced at higher processing stages. In ascending neurons, a focus on the range of low modulation frequencies was visible in the temporal MTFs, which describe the temporal locking of spikes to the signal envelope. To investigate the influence of stimulus rise time, we used rectangularly modulated stimuli instead of sinusoidally modulated ones. Unexpectedly, steep stimulus onsets had only small influence on the shape of MTF curves of 70% of neurons in our sample.
我们利用调制传递函数（MTF）研究了声音模式在蝗虫听觉通路上的处理方式。听觉感受器和初级样本地神经元的尖峰率不依赖于调制频率，而其他本地和上行神经元具有低通、带通或带阻特性。本地神经元的比率 MTF 动态范围较宽，可扩展至高于大多数上行神经元的调制频率。我们没有发现蝗虫听觉系统中可能存在调制频率滤波器组的迹象，而哺乳动物的听觉系统中存在这种滤波器组。一半神经元的滤波特性转变为全通型，调制深度降低 50%。与哺乳动物的报告相反，在较高的处理阶段，对小调制深度的敏感性并没有增强。在上行神经元中，在描述信号包络的尖峰与信号之间时间锁定的时间 MTF 中，可以看到对低调制频率范围的关注。为了研究刺激上升时间的影响，我们使用矩形调制刺激而不是正弦调制刺激。出乎意料的是，70%的神经元的 MTF 曲线形状仅受陡峭刺激起始的小影响。
