Xu J, Gooler D M, Feng A S
Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign 61801, USA.
J Comp Physiol A. 1996 Apr;178(4):435-45. doi: 10.1007/BF00190174.
Single-unit recordings were made from 143 neurons in the frog (Rana p. pipiens) inferior colliculus (IC) to investigate how free-field sound direction influenced neural responses to sinusoidal-amplitude-modulated (SAM) tone and/or noise. Modulation transfer functions (MTFs) were derived from 3 to 5 sound directions within 180 degrees of frontal field. Five classes of MTF were observed: low-pass, high-pass, band-pass, multi-pass, and all-pass. For 64% of IC neurons, the MTF class remained unchanged when sound direction was shifted from contralateral 90 degrees to ipsilateral 90 degrees. However, the MTFs of more than half of these neurons exhibited narrower bandwidths when the loudspeaker was shifted to ipsilateral azimuths. There was a decrease in the cut-off frequency for neurons possessing low-pass MTFs, an increase in cut-off frequency for neurons showing high-pass MTFs, or a reduction in the pass-band for neurons displaying bandpass MTFs. These results suggest that sound direction can influence amplitude modulation (AM) frequency tuning of single IC neurons. Since changes in periodicity of SAM tones alter both the temporal parameters of sounds as well as the sound spectrum, we examined whether directional effects on spectral selectivity play a role in shaping the observed direction-dependent AM selectivity. The directional influence on AM selectivity to both SAM tone and SAM noise was measured in 62 neurons in an attempt to gain some insight into the mechanisms that underlie directionally-induced changes in AM selectivity. Direction-dependent changes in the shapes of the tone and noise derived MTFs were different for the majority of IC neurons (55/62) tested. These data indicate that a spectrally-based and a temporally-based mechanism may be responsible for the observed results.
对青蛙（豹纹蛙）下丘（IC）中的143个神经元进行了单神经元记录，以研究自由场声音方向如何影响对正弦幅度调制（SAM）音调或噪声的神经反应。调制传递函数（MTF）由额前180度范围内的3至5个声音方向得出。观察到了五类MTF：低通、高通、带通、多通和全通。对于64%的IC神经元，当声音方向从对侧90度移至同侧90度时，MTF类别保持不变。然而，当扬声器移至同侧方位角时，这些神经元中超过一半的MTF带宽变窄。具有低通MTF的神经元截止频率降低，具有高通MTF的神经元截止频率增加，或具有带通MTF的神经元通带减小。这些结果表明，声音方向可影响单个IC神经元的幅度调制（AM）频率调谐。由于SAM音调周期性的变化会改变声音的时间参数以及声谱，我们研究了对频谱选择性的方向效应是否在塑造观察到的方向依赖性AM选择性中起作用。在62个神经元中测量了对SAM音调和SAM噪声的AM选择性的方向影响，以试图深入了解AM选择性方向诱导变化的潜在机制。对于大多数测试的IC神经元（55/62），音调及噪声衍生MTF形状的方向依赖性变化是不同的。这些数据表明，基于频谱和基于时间的机制可能是观察到的结果的原因。
