Implicit and explicit memory in Alzheimer's disease, fronto-temporal dementia and dementia with Lewy bodies

Explicit memory impairments differ between frontal lobe and hippocampal les ions. Implicit memory may involve temporal-parietal regions. The purpose of this study was to compare explicit and implicit visual memory performances in Alzheimer's disease (AD), in fronto-temporal dementia (FTD), and in dem entia with Lewy bodies (DLB). Explicit and implicit memory was assessed wit h a visual priming task adapted from the fragmented picture test in 45 subj ects: 11 patients with AD, 13 patients with DLB, 11 Pm patients and 11 cont rols. The patient groups did not differ for age (mean age 68 years), sex, l evel of education and severity of dementia assessed with the Mattis dementi a rating scale (mean DRS=132.3). At an early stage, DLB patients recognised explicitly fewer figures and made mom source errors than controls whereas AD and FTD patients did not differ from controls, DLB and AD patients had a decreased visual priming compared to controls whilst TD patients had a bet ter visual priming than AD patients. These results demonstrate impaired vis ual memory in DLB patients and more severe impairment of visual priming in AD than in DLB and FTD confirming that implicit memory may be more impaired in temporal parietal lobe damage than in frontal robe damage.