SEMANTIC MEMORY PROCESSING IN ALZHEIMER'S DISEASE

在记忆研究中，语义记忆和情景记忆有很大的区别（Tulving, 1972）。通常情况下，情景记忆被定义为对个人历史事件的记忆。相比之下，语义记忆是对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意义的认识中，不具有自传体成分。这种区别在区分阿尔茨海默病（AD）和正常衰老的影响方面尤为重要。正常老年人的记忆障碍似乎与情景记忆的衰退联系最为密切。相反，AD患者在情景记忆和语义记忆方面都表现出严重的损伤（Nebes, 1989）。例如，AD患者有找词困难（Nicholas, Obler, Albert & Helm- estrooks, 1985），命名图片物体的能力下降（Bayles & Tomoeda, 1983），并且难以记住最近呈现的文本的细节（Haut, Demarest, Keefover, & Rankin, 1994）。本应用程序的具体目的是测试AD中出现的语义记忆缺陷的两种解释。每种假说都提出了一种解释这些缺陷的具体机制。根据第一种假设，AD患者比正常老年人在识别语义关系方面有更多的困难。这种困难归因于评估语义关系的能力下降，而不是语义记忆基本组织的变化。第二个假设认为，当从语义记忆中检索概念时，AD患者通常会访问一组较窄的语义特征。以前对阿尔茨海默氏症记忆缺陷的解释范围很广，从假设一种共同的机制导致这些缺陷（Nebes & Brady, 1992）到提出一种机制，其影响仅限于特定的缺陷（Martin & Fedio, 1983）。本应用程序的更广泛目标是通过在先前几种解释的背景下检查当前的假设，开发一系列记忆缺陷的连贯描述，这些解释已经提出了解释这些缺陷的共同机制。这种策略的基本原理是，多种因素可能导致阿尔茨海默氏症的记忆缺陷，而在任务中的表现可能更好地理解为每个因素的相对影响，而不是一个单一的因素，负责大多数缺陷。该应用程序声称语义记忆处理的特定变化发生在AD的早期。如果这些内容是正确的，这些知识可以用来制定行为措施，促进AD的早期诊断。除了促进早期诊断外，这些研究的结果还可能促进可用于记录药物治疗对疾病进程影响的仪器的开发。

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.