SEMANTIC MEMORY DEFICITS ASSESSMENT IN DEMENTIA OF THE ALZHEIMER TYPE

GRASSO, L; PERAITA, H

Alzheimer´s Disease Research Journal

Nova Publishers

Lugar: Hauppauge, New York; Año: 2008 vol. 2

1935-2514

The study of the organization and structure of semantic memory and the research of the representation of this knowledge constitutes one of the topics of great interest in Cognitive Neuropsychology. It has been observed that, as a consequence of different lesions in the brain, the semantic memory system is selectively affected. In particular, it has been emphasized that there is a selective loss of the stored semantic information and dissociations among semantic categories. Because of the diffuse types of lesions, Dementia of the Alzheimer type (DAT) affects the semantic memory in a gradual and progressive manner. The present chapter evaluates the impairment of semantic knowledge of some natural categories and artifacts, and the attributes that organize them conceptually in patients with Alzheimer’s type dementia and in normal controls. A semantic memory battery was developed in Spanish to assess this kind of knowledge in DAT (EMSDA: Evaluation Battery for Semantic Memory Deterioration in Dementia of the Alzheimer type, Peraita et al. 2001). This battery includes sub-tests such as Verbal Fluency of category exemplars, Category Definitions, Picture Naming, Attribute Recognition, Spoken word/Picture Matching, Sentence Verification, and Semantic Analogies. Among the different tasks, the stimuli are complementary in the visual/verbal modality, and the production and comprehension process. In order to determine in which phase of the illness the deterioration of semantic memory appears, the results of the performance in the battery of a sample of 162 subjects (82 DAT and 80 healthy controls) were compared. The DAT group was further divided into two groups according to the severity of the disease (mild DAT N= 53; moderate DAT N= 29). We found that there is evidence of semantic deterioration in all tasks of the battery since very early stages of the disease. The Spoken Word/Picture Matching and Verbal Fluency task were the earliest impaired. We also describe the patterns of deterioration of conceptual – semantic relations, being the tendency of functional semantic relationships more preserved until the severe stages of the disease. There were no category specific dissociations. These results are relatively consistent with those obtained with EMSDA in a similar sample.