The nature of semantic memory deficits in Alzheimer's disease : evidence from event-related brain potentials and reaction time measures

The nature of semantic memory deficits in Alzheimer's disease: Evidence from event-related brain potentials and reaction time measures Semantic memory impairment is commonly observed in patients with dementia of the Alzheimer type (DAT); however the nature of the impairment is unclear. Some researchers argue that the deficit is a loss of information within semantic memory; whereas others argue that semantic memory impairment may result from a failure to access available information. The goal of this study was to investigate the nature of semantic memory deficits in patients with DAY Reaction time (RT) and the N400 event-related brain potential (ERP) were measured in a word-picture semantic priming paradigm. Age-related changes in semantic priming were assessed by comparing young and elderly adults; differences due to DAT were assessed by comparing elderly adults and DAT patients. For patients, pictures were classified as a function of the individual's naming ability to determine whether naming deficits reflected a failure to access a picture's name or a deterioration of its semantic representation. As expected, the young and elderly showed robust priming effects for both RT and ERP measures. DAT patients showed significant RT priming for named stimuli, yet no RT priming for unnamed stimuli. For ERP priming effects, the patient group was heterogeneous, with some patients showing ERP priming and others not. The results are discussed in terms of the access failure and deterioration hypotheses of semantic memory deficits in dementia of the Alzheimer type