CONCEPTUAL APRAXIA FROM LATERALIZED LESIONS

Models of praxis have posited two major components, production and con ceptual. Conceptual praxis disorders may occur in two domains: associa tive knowledge (tool-action associations such as hammer pound; tool-ob ject associations such as hammer nail) and mechanical knowledge such a s knowing the advantage that tools afford. Patients with Alzheimer's d isease not only have conceptual apraxia (CA) but carl dissociate CA fr om language deficits and from praxis production deficits (ideomotor ap raxia). These findings suggests that knowledge about tools (action sem antics) is independent of verbal semantics as well as movement represe ntations. To learn if conceptual praxis knowledge is stored in one hem isphere (right or left) and if associative and mechanical conceptual p raxis knowledge can be dissociated, we studied 29 right-handed subject s with unilateral strokes. Ten bad left-hemisphere damage with no ideo motor apraxia. Eleven had left-hemisphere damage with ideomotor apraxi a. There were eight right-hemisphere-damaged controls and 10 normal co ntrols. These subjects were given tests for conceptual apraxia. There was a significant difference between groups, the left-hemisphere group with ideomotor apraxia being most impaired on both the associative an d mechanical CA tests. There was a trend for associative and mechanica l knowledge to be dissociated. Although conceptual praxis representati ons are stored in the left hemisphere, analysis of lesion sites did no t reveal where in the left hemisphere they may be stored.