Aphasia, apraxia and the evolution of the language-ready brain

Background: The Mirror System Hypothesis offers the mirror system for grasping (i.e., neural mechanisms active for both execution and observation of grasping) as a neural "missing link'' between the brains of our non- human ancestors of 20 million years ago and the modern human language- ready brain, stressing the importance of manual gesture in the evolution of mechanisms supporting language. Aims: To assess the view that neural mechanisms for both praxis and language share an evolutionary relationship to the ancestral mirror system for grasping. Main Contribution: The praxis system receives a new analysis based on the attempt to link human praxis to computational models of execution and observation of grasping in the macaque as well as the analysis of parallels between language and praxis. Conclusions: The conceptual analysis presented here may prove insightful for clinicians seeking to relate and differentiate aphasia and apraxia.