N400 ABNORMALITIES IN UNMEDICATED SCHIZOPHRENIA DURING A LEXICAL DECISION TASK REVEALED BY LORETA (LOW RESOLUTION ELECTRO-MAGNETIC TOMOGRAPHY)

背景：事件相关电位（ERP）测量语言处理已报道在精神分裂症异常。然而，很少有研究评估未服药的患者，也没有很好地定义涉及这些缺陷的皮质系统。方法：采用erp对18例未服药的精神分裂症患者和18例年龄匹配的对照组进行词汇启动分析。视觉呈现成对的刺激。第一个刺激是一个词。第二个刺激要么是语义相关的，要么是与第一个单词无关的，要么是一个非单词。受试者决定第二个刺激是单词还是非单词。第二刺激诱发P200、N3530和后期正成分（LPC）。采用低分辨率电磁断层扫描（LORETA）对N400差异波形进行分析，评估两组脑皮层N400神经活动的分布。结果：精神分裂症患者N350和LPC潜伏期均延长，与语义加工减慢一致。从每种情况下的erp差异来衡量，N400启动效应在患者中有所降低。对照组双侧前额叶和双侧颞叶的N400电流密度显著。相比之下，患者显示N400电流密度降低，主要在双侧后颞区。结论：N400效应减弱表明精神分裂症患者对语义关系的敏感性降低，可能反映了语义网络连接异常。精神分裂症患者颞叶N400激活减少支持了颞叶结构作为精神分裂症语言和言语分离的神经基质。

Background: Event-related potential (ERP) measures of language processing have been reported to be abnormal in schizophrenia. However, few studies have evaluated unmedicated patients, nor are the cortical systems involved in these deficits well defined.Methods: ERPs were used to investigate lexical priming in eighteen unmedicated patients with schizophrenia and eighteen age-matched control subjects. Pairs of stimuli were visually presented. The first stimulus was a word. The second stimulus was either semantically related, unrelated to the initial word, or a non-word. The subject decided whether the second stimulus was a word or non-word. The second stimulus elicited the P200, N3530, and the late positive components (LPC). Low resolution electro-magnetic tomography (LORETA) was applied to the N400 difference waveforms to assess the brain cortical distribution of N400 neural activity for both groups.Results: Both N350 and LPC latency were prolonged in schizophrenia, consistent with slowed semantic processing. The N400 priming effect, measured from the difference ERPs in each condition, was reduced in patients. The N400 current density was prominent over the bilateral prefrontal and bilateral temporal in the control group. Patients, in contrast, showed decreased N400 current density, primarily over bilateral posterior temporal areas.Conclusion: The diminished N400 effect suggested reduced sensitivity to semantic relationships in schizophrenia, perhaps reflecting abnormal semantic network connectivity. Reduced temporal region N400 activation in schizophrenic patients supported the temporal lobe structures as the neural substrates subserving language and verbal disassociations in schizophrenia.