Abstract
We investigated semantic deficits in one case (case 1) with semantic dementia (SD) exhibiting Gogi aphasia due to frontotemporal lobar degeneration (FTLD) , and in one case (case 2) with progressive fluent aphasia exhibiting Wernicke-type aphasia that had diagnostic features for logopenic variant primary progressive aphasia due to atypical Alzheimer's disease (AD) , using several neuropsychological tests that included naming, object-to-word matching, and comprehension of multiple semantic attributes. Case 1 had bilateral anterior temporal lobe atrophy, and showed severe semantic memory impairment (SMI) . Case 2 had bilateral temporo-parietal lesions, and showed SMI specific for non-living things. They also exhibited different types of SMI in terms of semantic behavior for object use. Thus, we suggested that progressive fluent aphasia with SMI consisted of two variants, that is, anterior type (case 1) with bilateral anterior temporal lobe atrophy due to FTLD, and posterior type (case 2) with bilateral temporo-parietal degeneration due to AD.
Furthermore, we investigated the nature of SMI in 31 typical AD patients. They completed semantic tests sharing a common set of 16 target objects represented by pictures or words (names) , and we assessed consistent corresponding object-to-object (OTO) deficits among these tests. The AD group had significant OTO correspondence between a naming disability and a picture-to-word matching disability and between a picture-to-attribute matching disability and a word-to-attribute matching disability. However, neither naming disability nor picture-to-word matching disability had significant OTO correspondence with picture-to-attribute matching and word-to-attribute matching disabilities in the AD group. These results suggest that typical AD patients have a dual semantic deficit, that is, impaired object identification and loss of attributes of objects in an amodal semantic system.
