Many of the cognitive deficits seen in Alzheimer's disease have been attributed to a breakdown in the structure or function of semantic memory. Semantic memory consists of knowledge of semantic concepts, and verbal symbols, and the rule for their usage. Demented patients have been suggested to have lost those distinctive semantic features that constitute the specific meaning of concepts. It is not clear, however, whether this information has actually been lost, or whether the patients just have difficulty accessing it in situations in which they have to self initiate their own retrieval strategies. The present set of studies will examine semantic memory abilities in normal young, normal elderly, and demented elderly persons. We will investigate whether demented patients can retrieve and encode specific semantic features if they are given sufficient contextual support. We will also examine whether demented patients can process complex semantic concepts that are presented in the form of text. These experiments will determine whether patients with Alzheimer's disease have text-processing impairments beyond those associated with their memory decrement. These studies should help characterize the effects that dementia and normal aging have upon various aspects of semantic memory. Any differences in the effect of normal aging and dementia on semantic memory would be helpful in differential diagnosis. This would be especially true if we can demonstrate that some aspects of semantic memory are relatively resistent to the general cognitive deterioration seen in dementia. These abilities might then serve as a useful indicator of premorbid cognitive functioning in these patients, as well as a benchmark against which to evaluate rate of cognitive decline.
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