Ramachandran Ramnarayan, May Bradford J
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21205, USA.
J Neurophysiol. 2002 Nov;88(5):2251-61. doi: 10.1152/jn.00356.2002.
Decerebration allows single-unit responses in the central nucleus of the inferior colliculus (ICC) to be studied in the absence of anesthesia and descending efferent influences. When this procedure is applied to cats, three neural response types (V, I, and O) can be identified by distinct patterns of excitation and inhibition in pure-tone frequency-response maps. Similarities of the definitive response map features with those of projection neurons in the auditory brain stem have led to the proposal that the ICC response types are derived from different sources of ascending input that remain functionally segregated within the midbrain. Additional evidence for the existence of these hypothesized parallel processing pathways has been obtained in our previous investigations of the effects of interaural level differences, brain stem lesions, and pharmacological manipulations on physiologically classified units. This study extends our characterization of the functional segregation of single-unit activity in the ICC by investigating how sensitivity to interaural time differences (ITDs) is related to the response types that are observed in decerebrate cats. The results of these experiments support our parallel-processing model of the ICC by linking the ITD sensitivity of type V and I units to putative inputs from the medial superior olive and lateral superior olive and by showing that most type O units lack a systematic sensitivity to binaural temporal information presumably because their dominant ascending inputs arise from weakly binaural neurons in the dorsal cochlear nucleus.
去大脑状态可使在下丘中央核（ICC）中研究单单位反应时无需麻醉，且不受下行传出影响。当将此操作应用于猫时，通过纯音频率反应图中不同的兴奋和抑制模式可识别出三种神经反应类型（V、I和O）。确定性反应图特征与听觉脑干投射神经元的特征相似，这导致有人提出，ICC反应类型源自不同的上行输入源，这些输入源在中脑内仍保持功能分离。在我们之前关于双耳声级差、脑干损伤及药理学操作对生理分类单位影响的研究中，已获得了这些假设的平行处理通路存在的更多证据。本研究通过调查对双耳时间差（ITD）的敏感性与去大脑猫中观察到的反应类型之间的关系，扩展了我们对ICC中单单位活动功能分离的表征。这些实验结果通过将V型和I型单位的ITD敏感性与推测来自内侧上橄榄核和外侧上橄榄核的输入联系起来，并表明大多数O型单位对双耳时间信息缺乏系统性敏感性，这可能是因为它们主要的上行输入源自蜗背侧核中弱双耳神经元，从而支持了我们的ICC平行处理模型。
