Felix reaches up to catch a high line drive to left field and fires the ball off to Benji at home plate, who then tags the runner trying to score. For Felix to catch the ball and transfer it from his glove to his throwing hand, he needs to have a sense of where his hands are relative to one another and the rest of his body. This sort of information is subconsciously tracked in the body schema (or postural schema), (...) a representation of the current bodily posture that is updated on the basis of proprioceptive inputs. While the existence of the body schema in not in dispute, its origin is. After reviewing the competing proposals, I introduce the conceptual tools needed to move the debate forward and apply them to the question of the extent to which the body schema could be learned from perceptual input in utero. I argue that it could give rise to something recognizable as the body schema, though not quite rising to the level of the mature body schema. After considering the implications for further research on the origins of the body schema, I show how these results apply to other body representations, helping clarify the vexing question of the number, nature, and interactions among body representations in the brain. This theoretical work also promises to advance our understanding and treatment protocols for disorders affecting such body representations (e.g., anorexia nervosa). (shrink)

When efficiently used for action, tool becomes part of body, with effect on the spatial temporal movement parameters and body size perception. Until now, no previous investigation was reported about tool embodiment in Parkinson’s disease (PD), that is a neurological disease characterized by several sensory and motor symptoms affecting body and action. We enrolled fourteen individuals affected by PD and eighteen healthy individuals as controls. We studied the spatial-temporal parameters on self-paced free pointing movements task, via an optoelectronic system, before (...) and after a short training in which a 27 cm long rod was used to point toward a far target. Moreover, we investigated changes in estimation of arm length through the Tactile Estimation Task. After the tool use training, controls showed changes in spatial-temporal parameters: they were slower to perform movements and reported higher value of deceleration, respect to the baseline. However, such a difference did not emerged in the PD individuals. In the Tactile Discrimination Task, no difference emerged before and after the tool use training in both groups. Our results were suggestive of possible difficulties of tool embodiment process in PD. We discussed our results in relation to aberrant multisensory integration as well as in terms of the effect of PD sensory and motor symptoms on body schema plasticity. The present study points at a novel way to conceive PD sensory motor signs and symptoms, in terms of their effect on individuals’ body representation. (shrink)