Distinguishing early Alzheimer’s disease from normal ageing. A time course analysis of clustering and switching

Abstract

An impairment emerging in the early course of Alzheimer’s disease (AD) concerns the ability to produce words, reflected in verbal fluency (VF). Previously, a time analysis of correct words, repetitions, and intrusions has been done, and this study aims to expand this time analysis by introducing clustering and switching. 24 healthy young adults, 23 healthy older adults, and 19 patients with early AD performed phonemic and semantic VF tests. Clustering, together with the number of correct words identified semantic memory capacity, switching and errors reflected executive functions, and inter-item latencies indicated processing speed. Scores were analysed relative to 30 second periods. Healthy elderly had more repetitions in the first 30 seconds in phonemic VF, poorer clustering during the first 30 seconds, and poorer switching the last 30 seconds, both in semantic VF. Older age thus bring expected executive dysfunction. AD patients produced fewer words, more repetitions, and longer inter-item latencies during the first 30 seconds in both tasks, but especially in semantic VF. Also, phonemic clustering was impaired during the last 30 seconds. AD patients suffer from abnormal semantic memory detriments and slowing of processing speed, in addition to executive dysfunction. Phonemic clustering differentiated AD patients from healthy elderly, but only semantic VF impairments in memory and processing speed appeared abnormal in terms of time. Clustering and switching evaluated in a time course analysis shows potential of delineating possible abnormalities in VF in AD, and should be further investigated to increase the knowledge of VF in early AD.