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PLoS One. 2019 May 2;14(5):e0213732. doi: 10.1371/journal.pone.0213732. eCollection 2019.

Robot-assisted line bisection in patients with Complex Regional Pain Syndrome.

Author information

Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium.
Psychological Sciences Research Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Louvain-la-Neuve, Belgium.
Saint-Luc University Hospital, Brussels, Belgium.
Institute of Experimental and Clinical Research, Université catholique de Louvain, Brussels, Belgium.
Faculty of Motor Sciences, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Faculty of Motor Sciences, Université libre de Bruxelles, Brussels, Belgium.
Erasme University Hospital, Brussels, Belgium.


Complex Regional Pain Syndrome (CRPS) is characterized by pain, motor and inflammatory symptoms usually affecting one limb. Cognitive difficulties have been reported to affect patients' ability to represent, perceive and use their affected limb. It is debated whether these difficulties result from deficits in controlling goal-directed movements in space or from a learned strategy to protect the affected limb. In order to dissociate the two hypotheses, patients with upper-limb CRPS were asked to move with their unaffected hand towards visual targets projected at different positions on a horizontal semi-reflexive mirror. By means of a robotic handle placed below the screen, they were asked to move a cursor, to reach and cross lines at their estimated midpoint. In some of the stimulation series, the affected hand was placed below the mirror so that some lines appeared projected onto that hand. Vision of the hands and the robotic handle was preserved or prevented by opening or closing a shutter below the mirror. Lines were displayed on the mirror according to which part of the body was affected (ispi- vs. contralateral) and the actual position of the affected hand (inside vs. outside the workspace). Comparatively to control participants, CRPS patients generally biased their estimation by bisecting the lines towards their left side, irrelative of which part of the body was affected and the position of the affected hand, both in ipsi- and contralateral space, with only a few exceptions. Our results are in line with previous studies having described a visuospatial deficit in CRPS patients and discard the explanation of observed symptoms in terms of learned nonuse strategies, as only the unaffected hand was used to perform the task. It is suggested that CRPS patients can display difficulties to perform tasks requesting visuo-motor coordination, reflecting the complex cortical reorganization occurring in CRPS.

Conflict of interest statement

The authors have declared that no competing interests exist.

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