Praxis lateralization: Errors in right and left hemisphere stroke

Whereas the representations of skilled movements in most right handers are stored in the left: hemisphere, the right hemisphere's contribution to action planning remains unclear. We investigated error patterns in left (LHD) and right hemisphere damaged (RHD) subjects as well as normal control subjects (C) to determine if specific components of action programs may be processed by the right hemisphere or bilaterally represented. We had these subjects perform gestures to verbal command with the ipsilesional limb. Although the LHD group made significantly more qualitative errors than the C and RHD groups, the RHD subjects produced a number of apraxic errors. Specifically, the LHD group produced a wide range of spatiotemporal and conceptual errors for both transitive and intransitive gestures, while the RHD group made specific spatial and temporal errors primarily when performing transitive gestures. These findings support the postulate that the left hemisphere stores the spatiotemporal and conceptual representations of learned skilled movements, while several specific components of action programs, such as external configuration (limb orientation) and timing, may have bihemispheric representations.