Distinct memory profiles in Alzheimer's disease.

Memory impairment is a prominent defining feature of Alzheimer's disease (AD), yet the degree to which the profile of memory impairment is uniform across patients is not fully resolved. The study examined patterns of memory impairment in a large cohort of AD patients, with particular attention to the relationship between working and long-term declarative memory. Tests of working memory, visual and verbal recall and recognition, and recent personal memory were administered to 67 AD patients in the early to moderate stages of disease and to 30 age-matched controls. Performance on all measures was significantly poorer in patients than in controls. Factor analysis of test scores delineated five factors representing the domains of working memory, visual recall, verbal recall, recognition, and personal memory, indicating that these aspects of memory can break down separately. Cluster analysis revealed distinct memory profiles. Some patients showed predominant problems in working memory, with relatively superior long term retention, whereas other patients showed the reverse pattern. Qualitatively distinct profiles arose at comparable levels of severity. Problems in working memory, but not long term memory were associated with the presence of language and perceptuospatial deficits. The results reinforce previous findings that both working and long term memory failure contribute to the memory symptoms of AD patients, and demonstrate dissociations in memory breakdown across the cohort. The link between working memory and language performance, together with findings of posterior hemisphere abnormalities on neuroimaging, lead us to reassess the nature of working memory deficits in AD.