Apraxia in corticobasal degeneration

Corticobasal degeneration (CBD) is a degenerative disease that often presen ts with an asymmetric progressive ideomotor limb apraxia. Some apraxic subj ects may fail to perform skilled purposive movements on command because the y have lost the memories or representations that specify how these movement s should be performed (representational deficit). In contrast, other apraxi c subjects may have the movement representations but are unable to utilize the information contained in them to execute skilled purposive movements (p roduction-execution deficit). To learn if the apraxic deficit in CBD is ind uced by a representational or a production-execution deficit, we tested thr ee nondemented subjects with CBD on tasks requiring production of meaningfu l or meaningless gestures to command, gesture imitation, gesture discrimina tion, and novel gesture learning. A fourth subject with incomplete data als o is presented. The results suggest that the apraxia associated with CBD is initially induced by a production-execution defect with relative sparing o f the movement representations. (C) 1999 Academic Press.