Seghier Mohamed L, Price Cathy J
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London London, UK.
Front Psychol. 2012 Aug 13;3:281. doi: 10.3389/fpsyg.2012.00281. eCollection 2012.
This fMRI study investigated the functional heterogeneity of the core nodes of the default mode network (DMN) during language processing. The core nodes of the DMN were defined as task-induced deactivations over multiple tasks in 94 healthy subjects. We used a factorial design that manipulated different tasks (semantic matching or speech production) and stimuli (familiar words and objects or unfamiliar stimuli), alternating with periods of fixation/rest. Our findings revealed several consistent effects in the DMN, namely less deactivations in the left inferior parietal lobule during semantic than perceptual matching in parallel with greater deactivations during semantic matching in anterior subdivisions of the posterior cingulate cortex (PCC) and the ventromedial prefrontal cortex (MPFC). This suggests that, when the brain is engaged in effortful semantic tasks, a part of the DMN in the left angular gyrus was less deactivated as five other nodes of the DMN were more deactivated. These five DMN areas, where deactivation was greater for semantic than perceptual matching, were further differentiated because deactivation was greater in (i) posterior ventral MPFC for speech production relative to semantic matching, (ii) posterior precuneus and PCC for perceptual processing relative to speech production, and (iii) right inferior parietal cortex for pictures of objects relative to written words during both naming and semantic decisions. Our results thus highlight that task difficulty alone cannot fully explain the functional variability in task-induced deactivations. Together these results emphasize that core nodes within the DMN are functionally heterogeneous and differentially sensitive to the type of language processing.
这项功能磁共振成像（fMRI）研究调查了默认模式网络（DMN）核心节点在语言处理过程中的功能异质性。DMN的核心节点被定义为94名健康受试者在多个任务中任务诱发的失活。我们采用了析因设计，操纵不同的任务（语义匹配或言语产生）和刺激（熟悉的单词和物体或不熟悉的刺激），并与注视/休息期交替。我们的研究结果揭示了DMN中的几个一致效应，即在语义匹配时左顶下小叶的失活比感知匹配时少，同时后扣带回皮质（PCC）和腹内侧前额叶皮质（MPFC）前部在语义匹配时失活更多。这表明，当大脑从事费力的语义任务时，左角回中的DMN的一部分失活较少，而DMN的其他五个节点失活较多。这五个DMN区域，语义匹配时的失活比感知匹配时更大，它们进一步被区分，因为在以下方面失活更大：（i）相对于语义匹配，腹内侧前额叶皮质后部在言语产生时失活更大；（ii）相对于言语产生，后楔前叶和PCC在感知处理时失活更大；（iii）在命名和语义决策过程中，相对于书面单词，右顶下皮质在物体图片时失活更大。因此，我们的结果强调仅任务难度不能完全解释任务诱发失活中的功能变异性。这些结果共同强调，DMN内的核心节点在功能上是异质的，并且对语言处理类型有不同的敏感性。
