功能MRI研究左侧前额下回在汉字双音节真假词判断中的作用

目的采用快速事件相关功能MRI（event-related functional MRI，ER-fMRI）设计，比较人脑对真词和假词的认知加工过程。方法实验材料选用由2个汉字单音节构成的真词和假词。假词由真词中的单音语素（即对应的汉字词汇中的单个汉字音节）重新组合而成，用以控制亚词汇信息的平衡。在fMRI扫描过程当中，真词与假词的呈现顺序由伪随机方法确定，以听觉形式呈现给14名受试者，让其判断所听到的是真词还是假词。结果14名受试者听力词汇判断结果表明判断“假词”的速度明显要慢于判断“真词”的速度，而且“假词”判断的正确率明显要低于“真词”判断的正确率（平均错误率分别为9．9％和3．9％，平均反应时间分别为：1618ms和1143ms）。对真假词的判断激活了两侧额下回、颞上回、颞中回、距状回、舌回及左侧缘上回等脑区。同词汇判断的行为结果一致，左侧额下回对假词的反应明显强于其对真词的反应。结论左侧额下回在真假词任务判断中的作用，与形素到音素的转换过程无关，而是来源于对肯定和否定判断的不同反应模式。

Differential activity in left inferior frontal gyrus for pseudo and real words: an event-related functional MRI study on auditory lexical decision

Objective To study lexical processing of pseudo words and real words by using a fast event-related functional MRI (ER-fMRI) design. Methods Participants did an auditory lexical decision task on a list of pseudo-randomly intennixed real and pseudo Chinese two-character (or two-syllable) words. Pseudo words were constructed by recombining constituent characters of the real words to control for sublexical codes properties. Results The behavioral performance of fourteen participants indicated that response to pseudowords was significantly slower and less accurate than to real words ( mean error rate: 9. 9% versus. 3.9%, mean reaction time: 1618 ms versus 1143 ms ) . Processing of pseudo words and real words activated a highly comparable network of brain regions, including bilateral inferior frontal gyrus, superior, middle temporal gyrus, calcarine and lingual gyrus, and left supramarginal gyrus. Mirroring a behavioral lexical effect, left inferior frontal gyrus (IFG) was significantly more activated for pseudo words than for real words. Conclusion The results indicate that the processing of left inferior frontal gyrus in judging pseudo words and real words is not related to grapheme-to-phoneme conversion, but rather to making positive versus negative responses in decision making.