Hillery C M
Hear Res. 1984 May;14(2):129-43. doi: 10.1016/0378-5955(84)90012-1.
The whole nerve action potential (AP) from the auditory nerve and midbrain averaged evoked potential (AEP) were recorded in Hyla chrysoscelis and H. versicolor in response to synthesized amplitude-modulated stimuli with variable modulation frequencies (Fm). The AP from these frogs is similar to the potential described for mammals and showed a bandpass characteristic in its ability to follow sinusoidally amplitude-modulated (AM) sound stimuli. A lesioning study suggests that the midbrain AEP is a localized neural response of neurons near the ventral border of the torus semicircularis. The AEP is a complex waveform consisting of fast and slow components. The fast component encodes the temporal structure of acoustic stimuli and is used to measure temporal sensitivity in these two species. The AEP behaves like a low-pass filter with a cutoff frequency of 250 Hz when tracking AM signals. Threshold for detection requires a modulation depth of 8-12% of the total stimulus amplitude (delta I = 1.5-2.0 dB). Relative to the eighth nerve AP, the AEP displays an enhanced coding of AM signals when Fm less than 100 Hz, and a slightly inferior ability to code Fm above 250 Hz. The AEP reflects only that portion of the neural response that encodes amplitude fluctuations. In comparison to the range of amplitude fluctuations coded by single units in the rat inferior colliculus or by human evoked potential, the frog AEP codes higher rates of Fm. The proposal that these frogs process AM stimuli solely on the basis of amplitude fluctuations, and do not use spectral cues at higher modulation frequencies is considered. The AM sensitivity of the AEP, which encompasses most biologically relevant rates of amplitude fluctuation for the animal, and the limited frequency resolution of the periphery, lend support to this proposal. However, convergent spectral processing at higher auditory centers cannot be excluded by this study. Psychophysical tests will be required to determine whether both of these mechanisms may be operating during temporal information processing in anurans.
记录了金黄雨蛙和变色雨蛙听神经的全神经动作电位（AP）以及中脑平均诱发电位（AEP），以响应具有可变调制频率（Fm）的合成调幅刺激。这些青蛙的AP与哺乳动物所描述的电位相似，并且在跟随正弦调幅（AM）声音刺激的能力方面表现出带通特性。一项损伤研究表明，中脑AEP是半规管腹侧边缘附近神经元的局部神经反应。AEP是一个由快速和慢速成分组成的复杂波形。快速成分编码声学刺激的时间结构，并用于测量这两个物种的时间敏感性。在跟踪AM信号时，AEP的行为类似于截止频率为250 Hz的低通滤波器。检测阈值要求调制深度为总刺激幅度的8 - 12%（δI = 1.5 - 2.0 dB）。相对于第八神经AP，当Fm小于100 Hz时，AEP对AM信号的编码增强，而在编码高于250 Hz的Fm时能力略逊。AEP仅反映编码幅度波动的那部分神经反应。与大鼠下丘单个神经元编码的幅度波动范围或人类诱发电位相比，青蛙AEP编码更高的Fm速率。考虑了这些青蛙仅基于幅度波动处理AM刺激，而在更高调制频率下不使用频谱线索的提议。AEP的AM敏感性涵盖了动物最具生物学相关性的幅度波动速率，以及外周有限的频率分辨率，支持了这一提议。然而，本研究不能排除在更高听觉中枢的汇聚频谱处理。需要进行心理物理学测试来确定在无尾类动物的时间信息处理过程中这两种机制是否都在起作用。
