Body-tool integration: past, present, and future

Evolution has allowed humans to become proficient tool users, using tools to interact with their environment and functionally extend their limbs. Tools extend the sensorimotor boundaries of their user's body and in doing so modulate their body representations. In this chapter, we review the empirical evidence for this body-tool integration, focusing on the effects of basic tools as well as robotic limbs. We first explore how tools update the user's sensorimotor representations, reviewing behavioral and neural findings from the past decade, and novel research on development. Next, we focus on tool sensing, a new paradigm for investigating the ability to localize external tactile stimuli beyond the body. We then review how the sensorimotor system adapts to the use of robotic limbs, both in a medical and nonmedical context. Throughout the chapter, we also turn our attention to the past and the future, to discuss how evolution shaped our sensorimotor system and how humans now seem to be able to integrate robotic devices, further extending the limits of their sensorimotor system.