Reachability judgments in upper-limb segmentary exclusion syndrome explore action-related aspects of peripersonal space

Abstract Peripersonal space (PPS) refers to the multisensory representation of the space surrounding the body and is shaped by motor experience and body representation. Upper limb segmentary exclusion syndrome (UL-SES) is characterized by underuse of a limb segment without identifiable neurological lesion and is associated with altered body perception. Fifteen participants with UL-SES and 27 non affected participants completed a previously validated reachability judgment task assessing perceived maximum reachable distance (P-MRD) relative to objective maximum reachable distance (O-MRD). Body perception disturbances were evaluated using the BATH scale. Contrary to our hypothesis, PPS perception did not differ between affected and unaffected limbs in UL-SES in participants, nor between UL-SES and healthy participants. These findings may be explained by the focal nature of UL-SES, which mainly involved isolated fingers. However, body perception disturbances were significantly associated with reachability judgment accuracy on the affected side, with greater disturbances linked to more accurate estimations of reachable space. These results provide novel insights into the complex interplay between body representation, limb disuse, and PPS perception in UL-SES, offering potential avenues for therapeutic interventions and highlighting the enduring impact of limb exclusion on spatial perception.