Losing the beat: brain and behavior basis of human rhythm

我们与音乐互动的一个决定性特征是识别和移动到“节拍”的能力。这种复杂的能力是普遍的，在生命早期自发获得。然而，正如我们最近所展示的那样，有些人无法找到音乐中的节拍并与之同步，尽管他们有正常的听力，正常的运动和智力能力。这种疾病，我们称之为节拍性耳聋（一种新的先天性失乐症），提供了一个自然的实验，一个难得的机会来研究选择性认知缺陷是如何出现的，以及它是如何在大脑中表达的。本建议的目的是描述节拍性耳聋的功能和神经异常。 为此，我们将招募和测试异常（节拍聋）和对照组的成年人。将根据与诊断我们第一个病例相同的标准选择成年人。通过动作捕捉来衡量，其基本行为表现是身体动作与舞曲选择的同步性较差。这种紊乱似乎是节奏特有的，因为它使旋律音高的处理过程得以保留。因此，节拍性耳聋不同于最常见的先天性失音症，即影响音高处理的音高性耳聋。节拍聋和音高聋的表现的比较将有助于在控制贫乏的音乐体验的同时，对基于节拍的夹带进行分形。 在提案的第一部分，我们将研究如何在节拍跟踪赤字可以揭示人类基于节拍的夹带的特点。通常，人们在节拍之前敲击以消除由感觉运动反应引入的时间滞后。这种预期倾向被认为是人类独有的。我们将在这里测试是否拍聋的个人更积极的反应或表现出更强的影响，在预期的敲击节拍器样的刺激相比，控制和音高聋的表现首选的内源性利率。在第二部分中，我们将测试夹带机制的音乐特异性。我们预测，正常的参与者应该少敲键盘，唱歌的时候比正常说话的时候要少。相比之下，无论是自然的、有规律的语言还是歌曲，节拍性耳聋的人都应该同样糟糕，而音高性耳聋的表现将显示出相反的模式，因为歌曲包含干扰音高变化，所以在有规律的语言上表现最好。在第三部分中，神经夹带音乐将测量与一种新的电生理（EEG）技术，捕捉节拍相关的稳态诱发电位，以下的想法，自然的脑振荡可以夹带的听觉刺激的周期性。在节拍失聪者的大脑中，节拍的内部表征存在的证据应该是微弱的。一个有趣的替代方案是，脑电图显示正常的神经夹带在听，但不是在轻敲。这一发现表明，这种缺陷不是知觉的，而是由不良的大脑-运动耦合引起的。最后，在第四部分中，我们将使用几种磁共振成像（MRI）技术来寻找大脑异常，这些技术已被证明在音高性耳聋中提供了信息。节拍性耳聋是一个难得的机会，可以确定神经网络的哪些部分（从基底神经节到背侧运动前皮质）对夹带至关重要。 通过结合这些不同的神经心理学方法，该项目应该提供理论上的洞察力的神经生物学基础的人类节奏。

A defining characteristic of our interactions with music is the ability to identify and move to the “beat”. This complex ability is universal and spontaneously acquired early in life. Yet, as we have recently shown, some individuals fail to find the beat in music and to synchronize with it, despite having normal hearing, normal motor and intellectual abilities. This disorder, to which we refer as beat deafness (a new form of congenital amusia), provides a natural experiment, a rare chance to examine how a selective cognitive deficit emerges and how it is expressed in the brain. The goal of this proposal is to characterize the functional and neural anomalies of beat deafness. To this aim, we will recruit and test groups of abnormal (beat deaf) and control adults. Beat-deaf adults will be selected according to the same criteria as those used to diagnose our first case. Its essential behavioral manifestation is poor synchronization of body movements to selections of dance music, as measured by motion capture. The disorder appears specific to rhythm because it spares melodic pitch processing. Hence beat deafness is distinct from the most common form of congenital amusia, pitch deafness that affects pitch processing. The comparison of beat-deaf and pitch-deaf performance will serve to fractionate beat-based entrainment while controlling for impoverished musical experience. In PART I of the proposal, we will examine how deficits in beat-tracking can shed light on characteristics of human beat-based entrainment. Typically, people tap in advance of the beat to eliminate the time lag introduced by sensorimotor reaction. Such anticipatory tendencies are considered to be unique to humans. We will test here whether beat-deaf individuals are more reactive or exhibit stronger influences of preferred endogenous rates in anticipatory tapping to metronome-like stimuli as compared to control and pitch-deaf performance. In PART II, we will test the music-specificity of entrainment mechanisms. We predict that normal participants should tap less variably and with fewer asynchronies to song than to regular speech. In contrast, beat deaf individuals should be equally poor whether they tap on natural, regular speech or songs, and pitch deaf performance will show the opposite pattern with best performance on regular speech since songs contain interfering pitch variations. In PART III, neural entrainment to music will be measured with a novel electrophysiological (EEG) technique that captures beat-related steady-state evoked potentials, following the idea that natural brain oscillations can entrain to the periodicities of the auditory stimulus. In the brains of beat deaf listeners, the evidence for the presence of an internal representation of the beat should be weak. An interesting alternative is that the EEG reveals normal neural entrainment in listening but not in tapping. Such a finding would suggest that the deficit is not perceptual but arises from poor auditory-motor coupling. Finally, in PART IV, we will search for brain anomalies with several Magnetic Resonance Imaging (MRI) techniques that have proven to be informative in pitch deafness. Beat deafness represents a rare chance to identify which parts of the neural network (from the basal ganglia to the dorsal premotor cortex) are essential for entrainment. By combining these diverse neuropsychological methods, this project should provide theoretical insight on the neurobiological basis of human rhythm.