Pain, body, and space: What do patients with complex regional pain syndrome really neglect?

Space is an important dimension in perception. It helps to perceive the relative position between objects including one’s own body in order to guide interaction with the outer world. The brain is able to process spatial information according to different frames of reference. A first dissociation can be made between egocentric and allocentric representations. The egocentric, subject-centered frame of reference enables spatial representations of objects depending on their position relative to the perceiver’s body. In this case, left and right are defined according to the midline of the body or of specific body parts. In representations that depend on an allocentric frame of reference, the perception of position in space is independent of the observer. Space is then perceived in terms of positions between objects or between parts of the same objects. Another important distinction is the dissociation between personal, peripersonal and extrapersonal spaces. Personal space corresponds to the space of the body, peripersonal space to the immediate space surrounding the body allowing direct manipulation of proximal objects, and extrapersonal space to the far space in which objects are reached by limb movements.