NEURAL BASES OF SEMANTIC MEMORY

语义记忆是指关于物体、事实、概念、词语及其意义的知识。对语义记忆的神经基础的兴趣来自对语义记忆显著受损的患者的观察，尽管认知功能在其他方面是完整的。这种损害在退行性疾病中最常见：语义记忆障碍是阿尔茨海默病最早也是最突出的特征之一，而语义知识的丧失是与皮克氏病相关的一种被称为语义性痴呆的综合征的定义特征。单纯疱疹病毒性脑炎、大脑后动脉梗塞、缺氧缺血损伤和肿瘤切除的患者也观察到语义记忆障碍。这些观察结果导致了人们对语义记忆的神经基础的猜测，这得益于用于研究正常认知的现代神经成像技术的发展。这两种方法(病变研究和成像研究)已经确定了两个可能专门用于语义记忆的区域：左侧颞叶皮质和左侧前额叶皮质。基于对文献的分析和一些初步的发现，我们假设前额叶和颞叶皮质在语义记忆中起着截然不同的作用，并且前额叶皮质是选择竞争信息所必需的，而不是语义提取本身所必需的。该项目有四个主要目标：(1)证明前额叶皮质和颞叶皮质在语义记忆中的作用之间的分离；(2)从认知和神经角度更准确地描述颞叶皮质语义重复效应的性质；(3)进一步发展前额叶皮质辅助竞争信息选择的假设，并将这一假设与竞争替代方案区分开来；(4)用互补的成像和损伤方法为语义记忆的神经基础提供一致的证据。

Semantic memory refers to knowledge about objects, facts, concepts, and words and their meanings. Interest in the neural bases of semantic memory comes from observations of patients with striking impairments in semantic memory despite otherwise intact cognitive functioning. Such impairments are observed most commonly in degenerative diseases: semantic memory impairments are one of the earliest and most prominent features of Alzheimer's disease, and loss of semantic knowledge is the defining feature of a syndrome known as "semantic dementia", associated with Pick's disease. Impairments of semantic memory have also been observed in patients with herpes simplex encephalitis, posterior cerebral artery infarctions, hypoxic-ischemic injury, and tumor resection. These observations have led to speculation about the neural bases of semantic memory, aided by the development of modern neuroimaging techniques for studying normal cognition. These two methods (lesion studies and imaging studies) have identified two regions that may be specialized for semantic memory: left temporal cortex and left prefrontal cortex. Based on an analysis of the literature and some preliminary findings, we hypothesize that prefrontal and temporal cortex play quite distinct roles in semantic memory; and that prefrontal cortex is necessary for the selection of competing information, and not for semantic retrieval per se. The proposed project has four major goals: (1) to demonstrate a dissociation between the roles of prefrontal cortex and temporal cortex in semantic memory; (2) to describe in more precise terms, both cognitively and neurally, the nature of semantic repetition effects in temporal cortex; (3) to develop further the hypothesis that prefrontal cortex subserves the selection of competing information and to distinguish this hypothesis from competing alternatives; (4) to provide converging evidence as to the neural bases of semantic memory with complementary imaging and lesion methodologies.