Profiles of semantic knowledge impairment

Blaine S. Cloud

doi:10.17918/00000628

This research aims to elucidate relationships between knowledge stored in the brain and possible neuroanatomical substrates. It attempts to demonstrate that knowledge is distributed and can be divided phenomenologically and anatomically into perceptual and functional-associative components. Patients suffering from Alzheimer's Disease, Parkinson's Disease with dementia, and Ischaemic Vascular Disease served as experimental participants. Semantically impaired participants were divided into two groups according to the nature of their impairments: (1) primary breakdown of semantic structure, versus (2) primary inability to access otherwise intact semantic knowledge stores. Participants were administered a questionnaire that probed their knowledge of perceptual and functional-associative attributes of animals and tools. A 2 (group) x 2 (category) x 2 (attribute) analysis of variance demonstrated that patients with "knowledge degradation" were more impaired overall, and more impaired specifically on animal information as compared to "access" patients. It was predicted that the access patients would be impaired on associative-functional and tool information, but these predictions were not supported. The second hypothesis was that knowledge of animate objects is predicated upon perceptual information whereas knowledge of inanimate objects relies more heavily upon functional information. This hypothesis was not supported. Semantic dimensions were correlated with magnetic resonance imaging (MRI) indices. It was hypothesized that perceptual-animal knowledge would be dependent upon the integrity of posterior temporal cortex and functional-tool knowledge upon frontal lobe white matter tracts. However, semantic-neuroanatomic correlations did not reach significance. These findings support the notion that the brain's representations of knowledge are differentiated according to category membership and attribute type. Knowledge of tools and of functional attributes appears to be more impervious to loss in dementia than knowledge of animals and perceptual attributes. Degradation of knowledge leads to differential impairment working with animal knowledge whereas accessing impairment does not lead to preferential processing of either animate or tool knowledge. The relation between category and attribute level knowledge remains unclear but functional and perceptual attributes may be more closely associated with each other for tools than they are for animals. This may explain why tool knowledge was found to be more impervious to neuropathology.

Profiles of semantic knowledge impairment

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Profiles of semantic knowledge impairment

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