PROGRESSIVE IDEOMOTOR APRAXIA - EVIDENCE FOR A SELECTIVE IMPAIRMENT OF THE ACTION PRODUCTION SYSTEM

We report a patient with slowly progressive bilateral limb apraxial as sociated with an asymmetrical focal degenerative process of the pariet al lobes. Clinical assessment of praxis production suggested a strikin g deficit in controlling the spatiotemporal attributes of purposeful s killed limb movements, consistent with ideomotor apraxia. The precise nature of the action production impairment was further defined by obje ctive three-dimensional computergraphic analysis of transitive movemen ts which demonstrated significant kinematic deficits in spatial accura cy, timing, spatiotemporal coupling, and joint coordination. Gesture c omprehension and discrimination were spared. Furthermore, detailed eva luation of the conceptual praxis system revealed that despite an almos t complete inability to perform transitive movements accurately, abstr act knowledge of tool function and action was remarkably well preserve d. The critical dissociation between intact conceptual knowledge of ac tion and impaired movement execution documented in this case points to a fundamental competence/performance dichotomy in apraxia and provide s empirical support for cognitive models of praxis that divide the act ion system into distinct conceptual and production subcomponents. With in this theoretical framework, our patient's severe ideomotor apraxia is interpreted to represent a selective disruption of the action produ ction system. (C) 1995 Academic Press, Inc.