Effector-independence in the visuo-motor system: the case of foot action in people born without hands

Abstract

Many parts of the visuo-motor system are engaged in guiding the movement of the hands for daily tasks like reaching for and grasping objects. But to what extent is the organization of these regions dependent on the hand as a specific body part whose movement they guide, and to what extent are they organized for the grasping task, regardless of the body part used as an effector? We tested a unique population, people born without hands who use the feet as the primary effector (dysplasics), to address this question. In a functional neuroimaging experiment, dysplasics and typically-developed controls performed grasping and reaching actions with their primary effector, that is, the right foot for the dysplasics and right hand for the controls. Beyond primary sensorimotor cortices which showed selectivity for the hand and foot, we found a preference based on action type in parietal and frontal motor association areas including left anterior intraparietal sulcus and dorsal premotor cortex, regardless of the effector used. These results indicate that some motor association areas are organized based on abstract action functions independent of the specific sensorimotor parameters.