Poirier Pierre, Samson Frank K, Imig Thomas J
Department of Molecular and Integrative Physiology, Kansas University Medical Center, Kansas City 66160-7401, USA.
J Neurophysiol. 2003 May;89(5):2760-77. doi: 10.1152/jn.00640.2002.
We recorded high-best-frequency single-unit responses to free-field noise bursts that varied in intensity and azimuth to determine whether inferior colliculus (IC) neurons derive directionality from monaural spectral-shape. Sixty-nine percent of the sample was directional (much more responsive at some azimuths than others). One hundred twenty-nine directional units were recorded under monaural conditions (unilateral ear plugging). Binaural directional (BD) cells showed weak monaural directionality. Monaural directional (MD) cells showed strong monaural directionality, i.e., were much more responsive at some directions than others. Some MD cells were sensitive to both monaural and binaural directional cues. MD cells were monaurally nondirectional in response to tone bursts that lack direction-dependent variation in spectral shape. MD cells were unresponsive to noise bursts at certain azimuths even at high intensities showing that particular spectral shapes inhibit their responses. Two-tone inhibition was stronger where MD cells were unresponsive to noise stimulation than at directions where they were responsive. According to the side-band inhibition model, MD cells derive monaural directionality by comparing energy in excitatory and inhibitory frequency domains and thus should have stronger inhibitory side-bands than BD cells. MD and BD cells showed differences in breadth of excitatory frequency domains, strength of nonmonotonic level tuning, and responsiveness to tones and noise that were consistent with this prediction. Comparison of these data with previous findings shows that strength of spectral inhibition increases greatly between the level of the cochlear nucleus and the IC, and there is relatively little change in strength of spectral inhibition among the IC, auditory thalamus, and cortex.
我们记录了对强度和方位角变化的自由场噪声猝发的最高最佳频率单单元反应,以确定下丘(IC)神经元是否从单耳频谱形状中获得方向性。69%的样本具有方向性(在某些方位角比其他方位角反应强烈得多)。在单耳条件下(单侧耳塞)记录了129个具有方向性的单元。双耳定向(BD)细胞表现出较弱的单耳方向性。单耳定向(MD)细胞表现出较强的单耳方向性,即在某些方向比其他方向反应强烈得多。一些MD细胞对单耳和双耳定向线索都敏感。MD细胞对缺乏频谱形状方向依赖性变化的纯音猝发单耳无方向性。MD细胞在某些方位角即使在高强度下对噪声猝发也无反应,表明特定的频谱形状会抑制它们的反应。在MD细胞对噪声刺激无反应的地方,双音抑制比在它们有反应的方向更强。根据边带抑制模型,MD细胞通过比较兴奋性和抑制性频域中的能量来获得单耳方向性,因此应该比BD细胞具有更强的抑制性边带。MD和BD细胞在兴奋性频域宽度、非单调水平调谐强度以及对纯音和噪声的反应性方面存在差异,与这一预测一致。将这些数据与先前的研究结果进行比较表明,频谱抑制强度在蜗神经核水平和IC之间大幅增加,而在IC、听觉丘脑和皮层之间频谱抑制强度变化相对较小。