INSERM U1028-CNRS UMR5292, Centre de Recherche en Neurosciences de Lyon, Equipe Dynamique Cérébrale et Cognition, Centre Hospitalier le Vinatier, Batiment 452, 95 Bd Pinel, Bron, F-69500, France.
Brain. 2013 May;136(Pt 5):1639-61. doi: 10.1093/brain/awt082.
Congenital amusia is a lifelong disorder of music perception and production. The present study investigated the cerebral bases of impaired pitch perception and memory in congenital amusia using behavioural measures, magnetoencephalography and voxel-based morphometry. Congenital amusics and matched control subjects performed two melodic tasks (a melodic contour task and an easier transposition task); they had to indicate whether sequences of six tones (presented in pairs) were the same or different. Behavioural data indicated that in comparison with control participants, amusics' short-term memory was impaired for the melodic contour task, but not for the transposition task. The major finding was that pitch processing and short-term memory deficits can be traced down to amusics' early brain responses during encoding of the melodic information. Temporal and frontal generators of the N100m evoked by each note of the melody were abnormally recruited in the amusic brain. Dynamic causal modelling of the N100m further revealed decreased intrinsic connectivity in both auditory cortices, increased lateral connectivity between auditory cortices as well as a decreased right fronto-temporal backward connectivity in amusics relative to control subjects. Abnormal functioning of this fronto-temporal network was also shown during the retention interval and the retrieval of melodic information. In particular, induced gamma oscillations in right frontal areas were decreased in amusics during the retention interval. Using voxel-based morphometry, we confirmed morphological brain anomalies in terms of white and grey matter concentration in the right inferior frontal gyrus and the right superior temporal gyrus in the amusic brain. The convergence between functional and structural brain differences strengthens the hypothesis of abnormalities in the fronto-temporal pathway of the amusic brain. Our data provide first evidence of altered functioning of the auditory cortices during pitch perception and memory in congenital amusia. They further support the hypothesis that in neurodevelopmental disorders impacting high-level functions (here musical abilities), abnormalities in cerebral processing can be observed in early brain responses.
先天性失歌症是一种终身性的音乐感知和产生障碍。本研究采用行为测量、脑磁图和基于体素的形态测量学方法，探讨了先天性失歌症患者音高感知和记忆受损的大脑基础。先天性失歌症患者和匹配的对照组参与者完成了两个旋律任务（旋律轮廓任务和更简单的转调任务）；他们需要判断每对呈现的六个音的序列是否相同。行为数据表明，与对照组参与者相比，失歌症患者在旋律轮廓任务中的短期记忆受损，但在转调任务中没有。主要发现是，在对旋律信息进行编码时，失歌症患者大脑的早期反应可以追踪到音高处理和短期记忆缺陷。每个音符诱发的 N100m 的时、额部发生器在失歌症患者的大脑中异常募集。N100m 的动态因果建模进一步揭示了失歌症患者双侧听觉皮层的固有连接减少，听觉皮层之间的侧连接增加，以及相对于对照组患者右额颞后向连接减少。在保留间隔和旋律信息的检索过程中，也显示出这个额颞网络的异常功能。特别是，在保留间隔期间，右额区的诱导伽马振荡在失歌症患者中减少。通过基于体素的形态学测量，我们在失歌症患者的大脑中确认了右额下回和右上颞回的白质和灰质浓度的形态学异常。功能和结构脑差异的融合增强了失歌症患者大脑额颞通路异常的假设。我们的数据提供了先天性失歌症患者在音高感知和记忆过程中听觉皮层功能改变的初步证据。它们进一步支持了这样一种假设，即在影响高级功能（如音乐能力）的神经发育障碍中，可以在早期大脑反应中观察到大脑处理的异常。
