Department of Speech Language Hearing Sciences, Purdue University, West Lafayette, IN 47907-2038, USA.
Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, ON, Canada.
Neuropsychologia. 2012 Oct;50(12):2849-2859. doi: 10.1016/j.neuropsychologia.2012.08.013. Epub 2012 Aug 23.
Neural representation of pitch-relevant information at both the brainstem and cortical levels of processing is influenced by language or music experience. However, the functional roles of brainstem and cortical neural mechanisms in the hierarchical network for language processing, and how they drive and maintain experience-dependent reorganization are not known. In an effort to evaluate the possible interplay between these two levels of pitch processing, we introduce a novel electrophysiological approach to evaluate pitch-relevant neural activity at the brainstem and auditory cortex concurrently. Brainstem frequency-following responses and cortical pitch responses were recorded from participants in response to iterated rippled noise stimuli that varied in stimulus periodicity (pitch salience). A control condition using iterated rippled noise devoid of pitch was employed to ensure pitch specificity of the cortical pitch response. Neural data were compared with behavioral pitch discrimination thresholds. Results showed that magnitudes of neural responses increase systematically and that behavioral pitch discrimination improves with increasing stimulus periodicity, indicating more robust encoding for salient pitch. Absence of cortical pitch response in the control condition confirms that the cortical pitch response is specific to pitch. Behavioral pitch discrimination was better predicted by brainstem and cortical responses together as compared to each separately. The close correspondence between neural and behavioral data suggest that neural correlates of pitch salience that emerge in early, preattentive stages of processing in the brainstem may drive and maintain with high fidelity the early cortical representations of pitch. These neural representations together contain adequate information for the development of perceptual pitch salience.
在脑干和皮质处理水平上，与音高相关的信息的神经表示受到语言或音乐经验的影响。然而，脑干和皮质神经机制在语言处理的分层网络中的功能作用，以及它们如何驱动和维持经验依赖性重组尚不清楚。为了评估这两个音高处理水平之间的可能相互作用，我们引入了一种新的电生理方法来同时评估脑干和听觉皮层与音高相关的神经活动。研究人员记录了参与者对迭代波纹噪声刺激的脑干频率跟随反应和皮质音高反应，这些刺激在刺激周期性（音高显著性）上有所不同。使用没有音高的迭代波纹噪声的对照条件来确保皮质音高反应的音高特异性。将神经数据与行为音高辨别阈值进行比较。结果表明，神经反应的幅度系统地增加，并且随着刺激周期性的增加，行为音高辨别得到改善，这表明对显著音高的编码更加强大。在对照条件下没有皮质音高反应证实了皮质音高反应是特定于音高的。与每个单独的反应相比，脑干和皮质反应一起可以更好地预测行为音高辨别。神经数据和行为数据之间的紧密对应表明，在脑干的早期非注意处理阶段出现的音高显著性的神经相关物可能以高保真度驱动和维持早期皮质的音高表示。这些神经表示共同包含了发展感知音高显著性的足够信息。
