Rethinking actions: implementation and association.

Action processing allows us to move through and interact with the world, as well as understand the movements performed by other people. In recent years, there has been increasing interest in the semantics of actions as differentiated from the semantics of objects. However, as the understanding of action semantics has evolved, it is evident that the existing literature conflates two senses of the word 'action'-one that stems from studies of tool use and the other from event representation. In this paper, we suggest that this issue can be clarified by closely examining differences in how the human parietal and temporal cortices of the brain process action-related stimuli. By contrasting the posterior parietal cortex to the posterolateral temporal cortex, we characterize two complementary action systems in the human brain, each with its own specialization of function. We suggest that these two systems be referred to as the parietal Action Implementation System, and the posterolateral temporal Action Association System. While the frontoparietal system is concerned primarily with how we perform actions, and simulate others' actions, the temporal action system is more involved with processing actions from a third-person, conceptual standpoint. Recent work in cognitive neuroscience of perception and language, as well as the neuroanatomical organization of these brain regions support this distinction. We will discuss the implications of this work for cognition-, language-, and neuroscience-based action research.