Nieder A, Klump G M
Institut für Zoologie, Technische Universtät München, Lichtenbergstr. 4, D-85747 Garching, Germany.
Eur J Neurosci. 2001 Mar;13(5):1033-44. doi: 10.1046/j.0953-816x.2001.01465.x.
In the natural environment, acoustic signals have to be detected in ubiquitous background noise. Temporal fluctuations of background noise can be exploited by the auditory system to enhance signal detection, especially if spectral masking components are coherently amplitude modulated across several auditory channels (a phenomenon called 'comodulation masking release'). In this study of neuronal mechanisms of masking release in the primary auditory forebrain (field L) of awake European starlings (Sturnus vulgaris), we determined and compared neural detection thresholds for 20-ms probe tones presented in a background of sinusoidally amplitude modulated (10-Hz) noise maskers. Responses of a total of 34 multiunit clusters were recorded via radiotelemetry with chronically implanted microelectrodes from unrestrained birds. For maskers consisting of a single noise band centred around the recording site's characteristic frequency, a substantial reduction in detection threshold (21 dB on average) was found when probe tones were presented during envelope dips rather than during envelope peaks. Such effects could also explain results obtained for masking protocols where the on-frequency noise band was presented together with excitatory or inhibitory flanking bands that were either coherently modulated (in-phase) or incoherently modulated (phase-shifted). Generally, masking release for probe tones in maskers with flanking bands extending beyond the frequency range of a cell cluster's excitatory tuning curve was not substantially improved. Only some of the neurophysiological results are in agreement with behavioural data from the same species if only the average population response is considered. A subsample of individual neurons, however, could account for behavioural thresholds.
在自然环境中，必须在无处不在的背景噪声中检测声学信号。听觉系统可以利用背景噪声的时间波动来增强信号检测，特别是当频谱掩蔽成分在多个听觉通道上进行相干幅度调制时（一种称为“共调制掩蔽释放”的现象）。在这项对清醒的欧洲椋鸟（Sturnus vulgaris）初级听觉前脑（L区）掩蔽释放的神经元机制的研究中，我们确定并比较了在正弦幅度调制（10赫兹）噪声掩蔽背景下呈现的20毫秒探测音的神经检测阈值。通过无线电遥测，使用长期植入的微电极，从不受约束的鸟类中记录了总共34个多单元簇的反应。对于由围绕记录部位特征频率的单个噪声带组成的掩蔽器，当探测音在包络下降期间而不是在包络峰值期间呈现时，发现检测阈值大幅降低（平均降低21分贝）。这种效应也可以解释在掩蔽协议中获得的结果，在该协议中，中心频率噪声带与兴奋性或抑制性侧翼带一起呈现，这些侧翼带要么是相干调制（同相）要么是非相干调制（相移）。一般来说，对于掩蔽器中侧翼带超出细胞簇兴奋性调谐曲线频率范围的探测音，掩蔽释放并没有得到实质性改善。如果只考虑平均群体反应，只有一些神经生理学结果与来自同一物种的行为数据一致。然而，单个神经元的一个子样本可以解释行为阈值。
