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 acti on planning remains unclear. We investigated error patterns in left (LHD) a nd right hemisphere damaged (RHD) subjects as well as normal control subjec ts (C) to determine if specific components of action programs may be proces sed by the right hemisphere or bilaterally represented. We had these subjec ts 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 erro rs for both transitive and intransitive gestures, while the RHD group made specific spatial and temporal errors primarily when performing transitive g estures. These findings support the postulate that the left hemisphere stor es the spatiotemporal and conceptual representations of learned skilled mov ements, while several specific components of action programs, such as exter nal configuration (limb orientation) and timing, may have bihemispheric rep resentations.