Multisensory representations of the body and of the space around it (i.e. Peripersonal space, PPS) depend on the physical structure of the body, in that they are constructed from incoming multisensory signals from different body parts. After a sudden change in the physical structure of the body, such as limb amputation, little is known about how multimodal representations of the body and of the PPS adapt to loosing a part of the body, and how partially restoring the function of missing body part by means of prosthesis implantation affects these multimodal body representations.
We assessed body representation in a group of upper limb amputees by means of a tactile distance perception task, measuring the implicitly perceived length of the arm, and PPS representation by means of an audio-tactile interaction task, assessing the extension of the multisensory space where environmental stimuli interact with somatosensory processing. When patients performed the task on the amputated limb, without the prosthesis, the perceived arm length shrank, with a concurrent shift of PPS boundaries towards the stump. Wearing the prosthesis increased the perceived length of the stump and extended the boundaries of the PPS so to include the prosthetic hand. The representations of the healthy limb were comparable to those of healthy controls. These results suggest that a modification in the physical body affects multisensory body and PPS representations for the amputated side; such representations are further shaped if prostheses are used to replace the lost body part.