Amplitude-modulated (AM) signals represent important components of environmental sounds. While single-cell responses to AM tones in the central auditory system were often studied using repetitive modulation, owing to its presence in vocalization signals, the AM response has not been fully depicted in terms of receptive field in the stimulus domain. This study was aimed to characterize the receptive field of AM response with respect to nonrepetitive AM stimuli and to understand how complex acoustic signals may be coded in the brain. A novel AM stimulus was implemented with a random envelope and a systemic change in intensity across trials. From 393 single units recorded in the inferior colliculus (IC) of urethane-anesthetized rats, responses to the AM stimulus were first characterized in terms of dot-raster pattern. Three types of response were identified: type I showing a monotonic response to mainly the steady states of the AM envelope and type II to rising phases of the AM envelope with a clear intensity preference. Type III showed a mixed response of both type I and type II. A small number of units, called type IV, responded to both rising and falling phases of the modulation. Using perispike averaging, the AM receptive field, or "level temporal receptive field" (LTRF), was displayed in a "stimulus level versus perispike time" plane. The LTRF, particularly of the type II response, clearly revealed triggering features of the cell. The triggering features are consistent with the representation of the cell's response in a receptive space formed by the Cartesian axes of the velocity of amplitude modulation, the intensity of the sound, and the range of modulation. We therefore considered these stimulus parameters as the three basic determinants of the AM response in the auditory midbrain.

译文

:调幅(AM)信号代表环境声音的重要组成部分。尽管经常使用重复调制来研究中央听觉系统对AM音调的单细胞响应,由于其在发声信号中存在,但AM响应在刺激域的感受野方面尚未得到完整描述。这项研究旨在表征与非重复性AM刺激有关的AM反应的感受野,并了解如何在大脑中编码复杂的声音信号。实施了新型AM刺激,其随机包络和整个试验期间强度的系统性改变。从氨基甲酸乙酯麻醉大鼠下丘脑(IC)中记录的393个单位中,首先根据点阵模式表征了对AM刺激的反应。确定了三种类型的响应:I型对AM包络的稳态表现出单调响应,II型对AM包络的上升阶段具有明显的强度偏好。 III型表现出I型和II型的混合反应。少量的单元(称为IV型)对调制的上升阶段和下降阶段都做出了响应。使用峰峰值平均,在“刺激水平与峰峰值时间”平面中显示AM感受野或“水平时间感受野”(LTRF)。 LTRF(特别是II型反应)清楚地揭示了细胞的触发特征。触发特征与由振幅调制速度,声音强度和调制范围的直角坐标轴形成的接收空间中细胞响应的表示一致。因此,我们认为这些刺激参数是听觉中脑AM反应的三个基本决定因素。

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