Cognitive Neurology & Alzheimer's Disease Center, Northwestern University, Chicago, Illinois 60660, USA.
J Neurosci. 2009 Dec 16;29(50):15762-9. doi: 10.1523/JNEUROSCI.2912-09.2009.
Primary progressive aphasia (PPA), a selective neurodegeneration of the language network, frequently causes object naming impairments. We examined the N400 event-related potential (ERP) to explore interactions between object recognition and word processing in 20 PPA patients and 15 controls. Participants viewed photographs of objects, each followed by a word that was either a match to the object, a semantically related mismatch, or an unrelated mismatch. Patients judged whether word-object pairs matched with high accuracy (94% PPA group; 98% control group), but they failed to exhibit the normal N400 category effect (N400c), defined as a larger N400 to unrelated versus related mismatch words. In contrast, the N400 mismatch effect (N400m), defined as a larger N400 to mismatch than match words, was observed in both groups. N400m magnitude was positively correlated with neuropsychological measures of word comprehension but not fluency or grammatical competence, and therefore reflected the semantic component of naming. After ERP testing, patients were asked to name the same set of objects aloud. Trials with objects that could not be named were found to lack an N400m, although the name had been correctly recognized at the matching stage. Even accurate overt naming did not necessarily imply normal semantic processing, as shown by the absent N400c. The N400m was preserved in one patient with postsemantic anomia, who could write the names of objects she could not verbalize. N400 analyses can thus help dissect the multiple cognitive mechanisms that contribute to object naming failures in PPA.
原发性进行性失语症（PPA）是一种语言网络的选择性神经退行性疾病，常导致物体命名障碍。我们通过事件相关电位（ERP）的 N400 来研究 20 名 PPA 患者和 15 名对照者的物体识别与单词处理之间的相互作用。参与者观看物体的照片，每张照片后面都跟着一个词，这个词要么与物体匹配，要么语义上不相关，要么语义上不相关。患者对词-物对的匹配判断非常准确（PPA 组 94%；对照组 98%），但他们未能表现出正常的 N400 类别效应（N400c），即不相关的错配词比相关的错配词产生更大的 N400。相比之下，两组都观察到 N400 错配效应（N400m），即错配词比匹配词产生更大的 N400。N400m 的幅度与词汇理解的神经心理学测量呈正相关，而与流畅性或语法能力无关，因此反映了命名的语义成分。在 ERP 测试后，患者被要求大声说出同一组物体的名称。无法命名的物体的试验中发现缺乏 N400m，尽管在匹配阶段已经正确识别了名称。即使是准确的口头命名也不一定意味着正常的语义处理，因为 N400c 缺失。一名语义后性命名障碍患者保留了 N400m，她可以写出无法用言语表达的物体的名称。因此，N400 分析可以帮助剖析导致 PPA 中物体命名失败的多种认知机制。
