Envelope coding in the lateral superior olive. III. Comparison with afferent pathways
Envelope coding in the lateral superior olive. III. Comparison with afferent pathways
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DOI：
10.1152/jn.1998.79.1.253
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发表时间：
1998-01-01
影响因子：
2.5
通讯作者：
Yin, TCT
中科院分区：
文献类型：
--
作者：
Joris, PX;Yin, TCT
复杂高频声音空间定位的双耳线索为耳间级线索；md时差（ILDs和ITDs）。我们之前的研究表明，侧上橄榄（LSO）的细胞对正弦振幅调制（AM）信号包络中的过渡段敏感，调制频率仅与800 Hz相似。为了了解这种itd敏感性的局限性，我们在这里比较了来自耳蜗核和梯形体内侧核的LSO及其输入通路对单耳调制的反应。这些通路具有显著的功能和形态特化，暗示了对时间的适应。根据电生理特征确定传入细胞群，并将每个传入细胞群的平均放电率和与AM音调的同步与听觉神经纤维和LSO细胞进行比较。除了某些亚群的调制增益增加外，LSO传入神经的同步性对声压级（SPL）、调制深度和调制频率的依赖与听神经纤维非常相似。调制传递函数的截止频率分布与听神经的分布基本一致。从响应调制的相位作为调制频率的函数测量的群延迟，与特征频率和细胞类型有有序的依赖关系，与声压级的依赖关系很小。对调制宽带载波也获得了类似的响应。与传入信号相比，LSO细胞以更高的增益与单频调制刺激同步，但通常在更窄的调制频率范围内。考虑到传入和LSO细胞群的分散，单侧和对侧反应在延迟的截止频率和大小上很好地匹配。与传入信号相比，在高调制频率下，LSO细胞的平均放电速率下降。我们得出结论，LSO细胞表现出对itd敏感的有限调制频率范围不是由于传入通路上包膜信息的丢失，而是由于LSO水平上的收敛或突触后效应。LSO传入中包络锁相的忠实传递与其生理和形态适应一致，但这些适应与先前报道的生理过渡段的较小影响不相称，特别是与ild的影响相比。我们认为，这些适应已经进化到允许在两只耳朵的瞬时振幅波动的比较，而不是提取耳间的定时信息本身。
Binaural cues for spatial localization of complex high-frequency sounds are interaural level;md time differences (ILDs and ITDs). We previously showed that cells in the lateral superior olive (LSO) are sensitive to ITDs in the envelope of sinusoidally amplitude-modulated (AM) signals up to a modulation frequency of only similar to 800 Hz. To understand the limitations in this ITD-sensitivity, we here compare responses to monaural modulation in LSO and its input pathways, derived from cochlear nucleus and medial nucleus of the trapezoid body. These pathways have marked functional and morphological specializations, suggestive of adaptations for timing. Afferent cell populations were identified on the basis of electrophysiological signatures, and for each population, average firing rate and synchronization to AM tones were compared with auditory-nerve fibers and LSO cells. Except for an increase in modulation gain in some subpopulations, synchronization of LSO afferents was very similar to that in auditory nerve fibers in its dependency on sound pressure level (SPL), modulation depth, and modulation frequency. Distributions of cutoff frequencies of modulation transfer functions were largely coextensive with the distribution in auditory nerve. Group delays, measured from the phase of the response modulation as a function of modulation frequency, showed an orderly dependence on characteristic frequency and cell type and little dependence on SPL. Similar responses were obtained to a modulated broadband carrier. Compared with their afferents, LSO cells synchronized to monaurally modulated stimuli with a higher gain but often over a narrower range of modulation frequencies. Considering the scatter in afferent and LSO cell populations, ipsi-and contralateral responses were well matched in cutoff frequency and magnitude of delays. In contrast to their afferents, LSO cells show a decrease in average firing rate at high modulation frequencies. We conclude that the restricted modulation frequency range over which LSO cells show ITD-sensitivity does not result from loss of envelope information along the afferent pathway but is due to convergence or postsynaptic effects at the level of the LSO. The faithful transmission of envelope phase-locking in LSO afferents is consistent with their physiological and morphological adaptations, but these adaptations are not commensurate with the rather small effects of physiological ITDs reported previously, especially when compared with effects of ILDs. We suggest that these adaptations have evolved to allow a comparison of instantaneous amplitude fluctuations at the two ears rather than to extract interaural timing information per se.