Apraxia and the parietal lobes

I hypothesize that imitation of meaningless gestures and use of tool and objects depend on left parietal lobe integrity because of their demands on categorical apprehension of spatial relationships between multiple objects or between multiple parts of objects. For use of tools and objects the spatial relationships are between the hand, the tool, its recipient, and the material it acts upon. Categorical apprehension concentrates on features of these relations which determine mechanical interactions. For imitation of meaningless gestures, categorical apprehension of demonstrated gesture results in “body part coding” which reduces the visual appearance of the demonstrated gestures to simple spatial relationships between a limited set of discrete body parts. The hypothesis that the role of the left parietal lobe in apraxia concerns categorical apprehension of spatial relationships fits well with more general theories of parietal lobe function and hemisphere asymmetries.