Fishman Y I, Volkov I O, Noh M D, Garell P C, Bakken H, Arezzo J C, Howard M A, Steinschneider M
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Neurophysiol. 2001 Dec;86(6):2761-88. doi: 10.1152/jn.2001.86.6.2761.
Some musical chords sound pleasant, or consonant, while others sound unpleasant, or dissonant. Helmholtz's psychoacoustic theory of consonance and dissonance attributes the perception of dissonance to the sensation of "beats" and "roughness" caused by interactions in the auditory periphery between adjacent partials of complex tones comprising a musical chord. Conversely, consonance is characterized by the relative absence of beats and roughness. Physiological studies in monkeys suggest that roughness may be represented in primary auditory cortex (A1) by oscillatory neuronal ensemble responses phase-locked to the amplitude-modulated temporal envelope of complex sounds. However, it remains unknown whether phase-locked responses also underlie the representation of dissonance in auditory cortex. In the present study, responses evoked by musical chords with varying degrees of consonance and dissonance were recorded in A1 of awake macaques and evaluated using auditory-evoked potential (AEP), multiunit activity (MUA), and current-source density (CSD) techniques. In parallel studies, intracranial AEPs evoked by the same musical chords were recorded directly from the auditory cortex of two human subjects undergoing surgical evaluation for medically intractable epilepsy. Chords were composed of two simultaneous harmonic complex tones. The magnitude of oscillatory phase-locked activity in A1 of the monkey correlates with the perceived dissonance of the musical chords. Responses evoked by dissonant chords, such as minor and major seconds, display oscillations phase-locked to the predicted difference frequencies, whereas responses evoked by consonant chords, such as octaves and perfect fifths, display little or no phase-locked activity. AEPs recorded in Heschl's gyrus display strikingly similar oscillatory patterns to those observed in monkey A1, with dissonant chords eliciting greater phase-locked activity than consonant chords. In contrast to recordings in Heschl's gyrus, AEPs recorded in the planum temporale do not display significant phase-locked activity, suggesting functional differentiation of auditory cortical regions in humans. These findings support the relevance of synchronous phase-locked neural ensemble activity in A1 for the physiological representation of sensory dissonance in humans and highlight the merits of complementary monkey/human studies in the investigation of neural substrates underlying auditory perception.
有些音乐和弦听起来悦耳，即协和，而有些则听起来不悦，即不协和。亥姆霍兹关于协和与不协和的心理声学理论将不协和的感知归因于由构成音乐和弦的复合音相邻分音在听觉外周相互作用所引起的“拍音”和“粗糙度”感觉。相反，协和的特征是相对没有拍音和粗糙度。对猴子的生理学研究表明，粗糙度可能在初级听觉皮层（A1）中由与复合声音的幅度调制时间包络锁相的振荡神经元群体反应来表征。然而，锁相反应是否也构成听觉皮层中不协和表征的基础仍不清楚。在本研究中，在清醒猕猴的A1中记录了由不同程度协和与不协和的音乐和弦诱发的反应，并使用听觉诱发电位（AEP）、多单位活动（MUA）和电流源密度（CSD）技术进行评估。在平行研究中，直接从两名因药物难治性癫痫接受手术评估的人类受试者的听觉皮层记录了由相同音乐和弦诱发的颅内AEP。和弦由两个同时出现的谐波复合音组成。猴子A1中振荡锁相活动的幅度与音乐和弦的感知不协和程度相关。由不协和和弦（如小二度和大二度）诱发的反应显示出与预测差频锁相的振荡，而由协和和弦（如八度和纯五度）诱发的反应则显示很少或没有锁相活动。在颞横回记录的AEP显示出与在猴子A1中观察到的振荡模式惊人地相似，不协和和弦比协和和弦诱发更大的锁相活动。与在颞横回的记录不同，在颞平面记录的AEP没有显示出明显的锁相活动，这表明人类听觉皮层区域的功能分化。这些发现支持了A1中同步锁相神经群体活动与人类感觉不协和的生理表征的相关性，并突出了在研究听觉感知基础神经基质时互补性猴子/人类研究的优点。
