SEMANTIC MEMORY PROCESSING IN ALZHEIMER'S DISEASE

在对记忆的研究中，语义记忆和情景记忆之间有很大的区别(Tulving，1972)。通常，情节记忆被定义为对属于我们个人历史一部分的事件的记忆。相比之下，语义记忆是对关于世界的一般因素的记忆，这些因素体现在我们对单词和概念的含义的知识中，而这些词和概念没有自传成分。这一区别在区分阿尔茨海默病(AD)和正常衰老的影响方面特别相关。正常老年人的记忆障碍似乎与情景记忆的下降有最强烈的联系。相比之下，阿尔茨海默病患者在情景记忆和语义记忆方面都表现出严重的损害(尼贝斯，)。例如，AD患者有单词查找困难(Nicholas，Obler，Albert&Helm-Estarooks，1985)，命名图片对象的能力降低(Bayles&Tomoeda，1983)，以及难以记住最近呈现的文本中的细节(Haut，Demest，Keefover，&Rankin，1994)。这个应用程序的具体目的是测试对AD中发生的语义记忆缺陷的两种解释。每个假说都提出了一种特定的机制来解释这些缺陷。根据第一个假设，阿尔茨海默病患者比正常老年人更难识别语义关系。这一困难归因于评估语义关系的能力降低，而不是由于语义记忆的基本组织的改变。第二个假设认为，当从语义记忆中提取一个概念时，AD患者通常会获得一组较窄的语义特征。以前对阿尔茨海默病记忆缺陷的解释从认为这些缺陷是由一种共同的机制造成的(Nebes&Brady，1992)到提出了一种仅限于特定缺陷的机制(Martin&Fedio，1983)。这项申请的更广泛的目标是通过在先前几个解释的背景下检查当前的假设来对一系列记忆缺陷进行连贯的描述，这些解释提出了一个共同的机制来解释这些缺陷。这一策略的理论基础是，多种因素可能是导致AD记忆缺陷的原因，而任务中的表现可能更好地从每个因素的相对影响来理解，而不是从导致大多数记忆缺陷的单一因素的角度来理解。这个应用程序声称语义记忆处理的具体变化发生在AD的早期。如果这一内容是正确的，这一知识可以用来开发有助于AD早期诊断的行为测量方法。除了有助于早期诊断外，这些研究的结果还可能有助于开发可用于记录药物治疗对疾病进程的影响的工具。

Within research on memory, a broad distinction is made between semantic and episodic memory (Tulving, 1972). Typically, episodic memory is defined as memory for events that are part of our personal histories. In contrast, semantic memory is memory for general factors about the world that are embodied in our knowledge of the meanings of words, and concepts, that do not have an autobiographical component. This distinction is particularly relevant in distinguishing Alzheimer's disease (AD) from the effects of normal aging. Memory impairments in the normal elderly appear to be most strongly linked to a decline in episodic memory. In contrast, AD patients exhibit severe impairments both in episodic and semantic memory (Nebes, 1989). For example, AD patients have word finding difficulties (Nicholas, Obler, Albert & Helm- Estabrooks, 1985), a reduced ability to name pictured objects (Bayles & Tomoeda, 1983), and in difficulty in remembering details from recently presented text (Haut, Demarest, Keefover, & Rankin, 1994). The specific aim of this application is to test two explanations of the semantic memory deficits that occur in AD. Each hypothesis proposes a specific mechanism to explain these deficits. According to the first hypothesis, AD patients have more trouble identifying semantic relations than the normal old. This difficulty is attributed to a decreased ability to evaluated semantic relations rather than to a change in the basic organization of semantic memory. The second hypothesis claims that a narrower set of semantic features is typically accessed by AD patients when a concept is retrieved from semantic memory. Previous explanations of memory deficits in AD have ranged from accounts that assume that a common mechanism is responsible for these deficits (Nebes & Brady, 1992) to accounts that have advanced a mechanism whose effect is limited to a particular deficit (Martin & Fedio, 1983). The broader objective of this application is to develop a coherent account of a range of memory deficits by examining the current hypotheses within the context of several previous explanations that have advanced a common mechanism to explain these deficits. The rationale for this strategy is that a variety of factors are probably responsible for memory deficits in AD and performance within a task may be better understood in terms of the relative impact of each factor rather than in terms of a single factor that is responsible for most deficits. This application claims that specific changes in semantic memory processing occurs early in AD. If this content is correct, this knowledge could be used to develop behavioral measures that facilitate an early diagnosis of AD. In addition to facilitating early diagnosis, the results of these studies may facilitate the development of instruments that can be used to document the impact of drug treatments on the course of the disease.