Conceptual apraxia and semantic memory deficit in Alzheimer's disease: Twosides of the same coin?

This study was designed to examine the patterns of apraxic disturbances and the relationships between action knowledge and other measures of semantic knowledge about objects in PO well-characterized Alzheimer's disease (AD) p atients. Five tasks were used to assess components of action knowledge (act ion-tool relationships, pantomime recognition, and sequential organization of action) and praxis execution (actual use, pantomiming) according to the cognitive model of praxis. Three tasks (verbal comprehension, naming, and a visual semantic matching task) were used to assess verbal-visual semantics . Considering patterns of apraxia first, conceptual apraxia was found in 9 out of the 10 AD patients, suggesting that it is a common feature even in t he early stages of AD. Second, we found partly parallel deficits in tests o f action-semantic and verbal-visual semantic knowledge in 9 AD patients. Im paired action knowledge was found only in patients with a semantic :languag e deficit. These findings provide no evidence that "action semantics" may b e separated from other semantic information. Our results support the view o f a unitary semantic system, given that the representations of action-seman tic and other semantic knowledge of objects are often simultaneously disrup ted in AD.