I was excited to see the reference to this topical review in PAIN, as the subject is currently near and dear to my heart, and legs! CRPS is best known for its disabling sensory symptoms, including pain, allodynia, and abnormal skin temperature. Yet, motor dysfunction is common in CRPS and can result in major disability. In addition to weakness of the involved
limb, CRPS patients may develop symptoms akin to a neurological neglect-like syndrome, whereby the limb may feel
foreign ('cognitive neglect') and directed mental and visual attention is needed to move the limb ('motor neglect').
Published in PAIN: Journal of IASP; Also available on author's NOCION page.
Pain, body, and space: what do patients with complex regional pain syndrome really neglect?
Valéry Legrain a,b, Janet H. Bultitude c,d, Annick L. De Paepe a, Yves Rossetti d,e
a Department of Experimental Clinical and Health Psychology, Ghent University, Ghent, Belgiumb Institute of Neuroscience, Université catholique de Louvain, Louvain-la-Neuve and Brussels, Belgiumc Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UKd ImpAct, Centre de Recherche en Neurosciences de Lyon, Inserm U1028, CNRS UMR 5092, Université Claude Bernard Lyon 1, Bron, Francee Mouvement et Handicap, Hôpital Henry Gabrielle, Hospices Civils de Lyon, Lyon, France
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.
In humans, these dissociations have been documented by the neuropsychological investigations of patients affected by hemispatial neglect or hemineglect syndromes [1,9,10,23]. Hemineglect is an attentional deﬁcit after damage to one hemisphere characterized by an inability to explore and report stimuli on the side of space contralateral to the damaged hemisphere, in the absence of sensory and motor deﬁcits . The term hemi denotes the main feature of the disorder, stressing that hemineglect is not a global deﬁcit of space perception. It can affect different sensory systems and motor functions, in isolation or together .
3. An impaired perception of space in CRPS
resides, suggesting an impairment of a reference frame that is not dependent of the somatotopic representation of the body (i.e., personal frame) . It is therefore proposed that neglect-like symptoms in CRPS, and the underlying cortical changes, result from an implicit maladaptive reorganization of the sensory-motor system to avoid provocation of the affected limb, leading to an impaired representation of that limb .
Robinson et al.  have reported a single case of CRPS with impaired knowledge of spatial orientation for external objects. The patient was able to recognize and to name objects, but was unable to judge whether their orientation was canonical or not and was unable to reorient objects from noncanonical to canonical orientation. Surprisingly, this was especially marked along the horizontal axis (i.e., up vs down). The patient could correctly copy objects, but his copies were most of the time mirror reversed, as if, as outlined by the authors, the internal structure of visual objects was maintained but the main orientation axis was absent. This case ispuzzling because the deﬁcits of the patients cannot be explained by the opposition between affected vs. unaffected sides, nor by an impaired egocentric representation of space in which the viewer’s body is the main coordinate frame.