In this study we investigated how multisensory representations of the body (Body Schema; BS) and of the Peripersonal Space (PPS) adapt to changes in the structure of the physical body. Amputation and prosthesis implantation were tested as models of plasticity in upper limb amputees.
We studied the BS, by means of a tactile distance perception task, measuring the perceived length of the arm, and the PPS by means of an audio-tactile interaction task, measuring the extension of the multisensory space surrounding the arm. Subjects performed the tasks with the healthy and with the amputated limb, while wearing or not their prosthesis. BS and PPS representations for the healthy limb were comparable to those of controls; when patients performed the tasks without the prosthesis, the perception of the arm length was reduced and the boundaries of the PPS shifted towards the stump. Conversely, wearing the prosthesis increased the perceived length of the arm and extended PPS boundaries so to include the prosthetic hand. These results suggest that when amputees wear their prosthesis, they incorporate the prosthetic hand such as it belongs to their own body, thus partially restoring the boundaries of body and space representations for the amputated side.