Semantic memory impairment in schizophrenia--deficit in storage or access of knowledge?

This study evaluates whether patients with schizophrenia have a degraded memory store for semantic knowledge. 20 patients with a chronic history of schizophrenia and evidence of cognitive impairment were selected, since the literature indicates that this subgroup is most likely to manifest a degraded semantic knowledge store. Their profile of semantic memory impairments was compared to that of a group of Alzheimer's Dementia (AD) patients (n=22), who met neuropsychological criteria for degraded semantic store. Both groups were matched for Performance IQ. 15 elderly healthy controls were also included in the study. The AD and schizophrenia groups produced substantially different profiles of semantic memory impairment. This is interpreted as indicating that the semantic impairments in this subgroup of patients with schizophrenia do not result from a degraded store. This is corroborated by an analysis of the data using other neuropsychological criteria for determining degraded store. We conclude that there is little evidence for a classic degradation of semantic knowledge in schizophrenia, and it appears that impairments result from an inability to use semantic knowledge appropriately, particularly when selection of salient semantic relations is required.