Cognitive Neuroimaging Unit, NeuroSpin, CEA/SAC/DSV/I2BM, F-91191 Gif-sur-Yvette, France.
Cereb Cortex. 2010 Sep;20(9):2244-51. doi: 10.1093/cercor/bhp290. Epub 2010 Jan 4.
Most bilinguals understand their second language more slowly than their first. This behavioral asymmetry may arise from the perceptual, phonological, lexicosemantic, or strategic components of bilingual word processing. However, little is known about the neural source of such language dominance and how it is regulated in the bilingual brain. Using functional magnetic resonance imaging, we found that unconscious neural priming in bilingual word recognition is language nonselective in the left midfusiform gyrus but exhibits a preference for the dominant language in the left posterior middle temporal gyrus (MTG). These early-stage components of reading were located slightly upstream of the left midlateral MTG, which exhibited enhanced response during a conscious switch of language. Effective connectivity analysis revealed that this language switch is triggered by reentrant signals from inferior frontal cortex and not by bottom-up signals from occipitotemporal cortex. We further confirmed that magnetic stimulation of the same inferior frontal region interferes with conscious language control but does not disrupt unconscious priming by masked words. Collectively, our results demonstrate that the neural bottleneck in the bilingual brain is a cross-language asymmetry of form-meaning association in inferolateral temporal cortex, which is overcome by a top-down cognitive control for implementing a task schema in each language.
大多数双语者理解第二语言的速度比第一语言慢。这种行为上的不对称性可能源于双语者的词汇处理的感知、语音、词汇语义或策略成分。然而，对于这种语言优势的神经源以及它在双语大脑中是如何调节的，我们知之甚少。我们使用功能磁共振成像发现，在双语者的单词识别中，无意识的神经启动在左侧中脑回是语言非选择性的，但在左侧后颞中回（MTG）中表现出对主导语言的偏好。阅读的这些早期阶段成分位于左侧中侧 MTG 的稍上游，在语言的有意识转换期间表现出增强的反应。有效连通性分析表明，这种语言转换是由来自下额叶皮层的折返信号触发的，而不是由来自枕颞叶皮层的底向上信号触发的。我们进一步证实，对同一下额叶区域的磁刺激会干扰有意识的语言控制，但不会通过掩蔽词破坏无意识的启动。总的来说，我们的结果表明，双语者大脑中的神经瓶颈是外侧颞叶中形式与意义的跨语言不对称性，这种瓶颈通过自上而下的认知控制来克服，以在每种语言中实施任务图式。
