Program in Neuroscience, Gustavus Adolphus College, 800 West College Ave, St. Peter, MN 56082, USA.
Hear Res. 2011 Oct;280(1-2):109-21. doi: 10.1016/j.heares.2011.04.014. Epub 2011 May 4.
Anuran auditory nerve fibers (ANF) tuned to low frequencies display unusual frequency-dependent adaptation which results in a more phasic response to signals above best frequency (BF) and a more tonic response to signals below. A network model of the first two layers of the anuran auditory system was used to test the contribution of this dynamic peripheral adaptation on two-tone suppression and amplitude modulation (AM) tuning. The model included a peripheral sandwich component, leaky-integrate-and-fire cells and adaptation was implemented by means of a non-linear increase in threshold weighted by the signal frequency. The results of simulations showed that frequency-dependent adaptation was both necessary and sufficient to produce high-frequency-side two-tone suppression for the ANF and cells of the dorsal medullary nucleus (DMN). It seems likely that both suppression and this dynamic adaptation share a common mechanism. The response of ANFs to AM signals was influenced by adaptation and carrier frequency. Vector strength synchronization to an AM signal improved with increased adaptation. The spike rate response to a carrier at BF was the expected flat function with AM rate. However, for non-BF carrier frequencies the response showed a weak band-pass pattern due to the influence of signal sidebands and adaptation. The DMN received inputs from three ANFs and when the frequency tuning of inputs was near the carrier, then the rate response was a low-pass or all-pass shape. When most of the inputs were biased above or below the carrier, then band-pass responses were observed. Frequency-dependent adaptation enhanced the band-pass tuning for AM rate, particularly when the response of the inputs was predominantly phasic for a given carrier. Different combinations of inputs can therefore bias a DMN cell to be especially well suited to detect specific ranges of AM rates for a particular carrier frequency. Such selection of inputs would clearly be advantageous to the frog in recognizing distinct spectral and temporal parameters in communication calls.
蛙类听觉神经纤维（ANF）对低频的调谐显示出异常的频率依赖性适应，这导致对最佳频率（BF）以上的信号产生更相位的反应，对 BF 以下的信号产生更紧张的反应。使用蛙类听觉系统前两层的网络模型来测试这种动态外围适应对双音抑制和幅度调制（AM）调谐的贡献。该模型包括一个外围三明治组件、漏电积分和放电细胞，通过信号频率加权的非线性阈值增加来实现适应。模拟结果表明，频率依赖性适应既是产生 ANF 和背侧髓质核（DMN）细胞高频侧双音抑制的必要条件，也是充分条件。似乎抑制和这种动态适应都具有共同的机制。ANF 对 AM 信号的反应受到适应和载波频率的影响。对 AM 信号的向量强度同步随适应的增加而提高。在 BF 处对载波的尖峰率反应是预期的平坦函数，带有 AM 率。然而，对于非 BF 载波频率，由于信号边带和适应的影响，响应表现出弱带通模式。DMN 接收来自三个 ANF 的输入，当输入的频率调谐接近载波时，那么率响应是低通或全通形状。当大多数输入偏向载波上方或下方时，则观察到带通响应。频率依赖性适应增强了 AM 率的带通调谐，特别是当输入的响应对于给定的载波主要是相位时。因此，不同的输入组合可以使 DMN 细胞偏向于特别适合检测特定载波频率的特定 AM 率范围。这种输入的选择显然对青蛙在识别通信呼叫中的独特光谱和时间参数是有利的。
