Department of Psychology, Tulane University, New Orleans, LA, USA.
Brain Res. 2010 Oct 8;1355:126-40. doi: 10.1016/j.brainres.2010.07.099. Epub 2010 Aug 5.
The N400 is an event-related potential (ERP) component that is elicited by semantically meaningful stimuli; one of its defining characteristics is that it is amplified for sentence completions that are semantically unexpected or incongruous with the preceding context. Some prior reports using visual sentence reading paradigms have suggested that there may also be a Cz-centered P400 (a P400cz) that is also responding to semantic congruity manipulations, distinct from the classic Pz-centered N400 (the N400pz). In the present experiment, sentences were presented visually one word at a time, and half of the sentences ended with a semantically incongruent ending. High-density 129-channel event-related potential data were recorded from 26 participants. A combination of temporo-spatial principal components analysis (PCA) and item averaging was applied to decompose the waveforms. The presence of the P400cz was confirmed. The P400cz was much more sensitive to congruity and somewhat more sensitive to cloze probability than the N400pz. The separation of the N400 semantic effect into these two portions is consistent with both MEG studies and intracranial studies. The data suggest that the N400pz has its major source in the bilateral anterior medial temporal lobe (AMTL) whereas it is suggested that the P400cz has its major source in the medial parietal region. It is further suggested that whereas the N400pz process appears to be semantic in nature, some prior reports suggest that the P400cz reflects a general sequential expectancy system.
N400 是一种事件相关电位（ERP）成分，由语义上有意义的刺激引发；其定义特征之一是，对于语义上出乎意料或与前文语境不一致的句子完成，它会被放大。一些先前使用视觉句子阅读范式的报告表明，可能还有一个 Cz 中心化的 P400（P400cz），它也对语义一致性操纵做出反应，与经典的 Pz 中心化 N400（N400pz）不同。在本实验中，句子逐字地以视觉方式呈现，并且一半的句子以语义上不一致的结尾结束。从 26 名参与者记录了高密度 129 通道事件相关电位数据。采用时-空域主成分分析（PCA）和项目平均相结合的方法对波形进行分解。证实了 P400cz 的存在。与 N400pz 相比，P400cz 对一致性更为敏感，对 cloze 概率也稍微敏感。将 N400 语义效应分为这两个部分，这与 MEG 研究和颅内研究一致。数据表明，N400pz 的主要来源在双侧前内侧颞叶（AMTL），而 P400cz 的主要来源在内侧顶叶区域。进一步表明，N400pz 处理过程似乎具有语义性质，而先前的一些报告表明 P400cz 反映了一般的顺序预期系统。
