The Key Dimensions of Human Action: Content and Form

Human action, both in execution and observation, is characterized by two fundamental attributes: the action goal (the "what") and its vitality form (VF), namely the "how" an action is performed. Over the past three decades, substantial progress has been made in elucidating the neural bases of action goals. Converging evidence identifies a parieto-frontal network, possibly extending to additional brain regions, which encodes the goal-related content of both observed and executed actions (the mirror circuit). In contrast, considerably less attention has been devoted to the neural mechanisms underlying vitality forms. Nevertheless, growing evidence indicates that VFs are processed by a distinct insulo-cingulate network. Together, the parieto-frontal and insulo-cingulate circuits constitute a functional architecture that integrates goal representation with affective-motor expression. This integration enables social understanding and supports adaptive interpersonal behavior. The present review is organized into three sections. First, we examine the neural circuits underlying action goals and vitality forms. Second, we review evidence that interactions between these two neural systems underwrite action and its observation. Third, we discuss the role of vitality forms in the development of humanoid robots.