Imig T J, Bibikov N G, Poirier P, Samson F K
Department of Molecular and Integrative Physiology, Kansas University Medical Center, Kansas City, Kansas 66160-7401, USA.
J Neurophysiol. 2000 Feb;83(2):907-25. doi: 10.1152/jn.2000.83.2.907.
We tested two hypotheses to determine whether dorsal cochlear nucleus (DCN) neurons are specialized to derive directionality from spectral notches: DCN neurons exhibit greater spectral-dependent directionality than ventral cochlear nucleus (VCN) neurons, and spectral-dependent directionality depends on response minima (nulls) produced by coincidence of best frequency (BF) and spectral-notch center frequency. Single-unit responses to 50-ms noise and tone bursts were recorded in barbiturate-anesthetized cats (BFs: 4-37 kHz). Units were classified using BF tone poststimulus time histograms. Pauser, onset-G (type II interneurons), and some chopper units were recorded from the DCN. Primary-like, onset-CIL (onset other than onset-G), and most choppers in the sample were recorded from the VCN. Many pauser and onset-G units were highly directional to noise. Chopper, onset-CIL, and primary-like units (collectively referred to as C-O-P units) were not. The difference in directionality depends on a monaural mechanism as pausers were more directional to monaural noise than C-O-P units. Contralateral inhibition produced a small increase in pauser directionality to noise simulation but had no effect on directionality of C-O-P units. Pauser and C-O-P units exhibited similar low directionality to BF tone, showing that the difference in noise directionality between groups depends on spectral cues. These results show that spectral-dependent directionality is a DCN specialization. Azimuth functions of highly directional units exhibited response nulls, and there was a linear relationship between BFs in the range of 8-13 kHz and azimuthal locations of nulls. This relationship parallels the known spatial distribution of spectral-notch center frequencies on the horizontal plane. Furthermore spatial receptive fields of pausers show response nulls that follow the expected diagonal trajectory of the spectral notch in this frequency range. These results show that DCN spectral-dependent directionality depends on response nulls produced by coincidence of unit BF and spectral-notch center-frequency.
我们检验了两个假设，以确定蜗背侧核（DCN）神经元是否专门从频谱凹口获取方向性：DCN神经元比蜗腹侧核（VCN）神经元表现出更大的频谱依赖性方向性，并且频谱依赖性方向性取决于最佳频率（BF）与频谱凹口中心频率重合所产生的反应最小值（零点）。在巴比妥麻醉的猫（BFs：4 - 37 kHz）中记录对50毫秒噪声和纯音脉冲的单单位反应。使用BF纯音刺激后时间直方图对单位进行分类。从DCN记录到了暂停型、起始-G型（II型中间神经元）和一些切迹型单位。样本中的初级样、起始-CIL型（非起始-G型的起始）和大多数切迹型单位是从VCN记录到的。许多暂停型和起始-G型单位对噪声具有高度方向性。切迹型、起始-CIL型和初级样单位（统称为C - O - P单位）则不然。方向性的差异取决于单耳机制，因为暂停型单位对单耳噪声的方向性比C - O - P单位更强。对侧抑制使暂停型单位对噪声模拟的方向性略有增加，但对C - O - P单位的方向性没有影响。暂停型和C - O - P单位对BF纯音表现出相似的低方向性，表明两组之间噪声方向性的差异取决于频谱线索。这些结果表明，频谱依赖性方向性是DCN的一种特性。高度方向性单位的方位函数表现出反应零点，并且在8 - 13 kHz范围内的BFs与零点的方位位置之间存在线性关系。这种关系与水平面上频谱凹口中心频率的已知空间分布相似。此外，暂停型单位的空间感受野显示出反应零点，这些零点遵循该频率范围内频谱凹口预期的对角线轨迹。这些结果表明，DCN频谱依赖性方向性取决于单位BF与频谱凹口中心频率重合所产生的反应零点。
