Body schema boundaries are formed by sensorimotor body-environment distinction

The basic self-perception of being a body that is delimited and in this sense distinct from the environment should be defined by the boundaries of the body schema. The body schema was and is extensively investigated in humans, e.g., in studies on neurological disorders, as well as in animals, e.g., in studies on somatosensory receptive fields. Yet, it was so far not investigated how the boundaries of the body schema are formed. We have investigated if these subjective body boundaries result from the distinction of body and environment sensations regarding their predictability by the motor representation of active bodily self-motion. In a first study, we enabled healthy humans to control with their physical body a life-sized virtual body that was mirroring their movements in extrapersonal space. In a second study, we asked human subjects to control either such a mirror-avatar or one that was additionally unpredictably shaking. We found that the remote motor control of the mirror-avatar caused the body schema boundaries to decline while inhibiting the distinction of auto-kinesthetic sensations that are, and visual motion sensations that are not, directly predicted by the motor representation of active bodily self-motion. This sensorimotor body-environment distinction was instead intensified by the remote motor control of the shaking-avatar, which fortified the body schema boundaries. Our findings suggest that the distinction of sensations that are, and those that are not, directly predicted by motor representation based on their motor predictability is forming the human body schema boundaries. This sensorimotor body-environment distinction corresponds to the previously suggested self-world distinction that is regarded as fundamental for motor control to arise from sensorimotor integration and for body self-perception in general. Such a sensorimotor distinction and the body schema boundaries that it forms may accordingly affect the sense of agency and various other body self-perception components such as the sense of bodily self-identification and self-location