Brain Advance Access originally published online on September 14, 2009
Brain 2009 132(11):3142-3151; doi:10.1093/brain/awp224
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Space-based, but not arm-based, shift in tactile processing in complex regional pain syndrome and its relationship to cooling of the affected limb
1 PaiN Group & Department of Physiology, Anatomy & Genetics, University of Oxford, UK and Prince of Wales Medical Research Institute & School of Medical Sciences, University of New South Wales, Sydney, Australia 2 Department of Psychology, University of Milano-Bicocca, P.zza dell'Ateneo Nuovo 1, 20126 Milano, Italy 3 Department of Experimental Psychology, Oxford University, South Parks Road, Oxford OX1 3UD, UK
Correspondence to: G. Lorimer Moseley, Prince of Wales Medical Research Institute, Cnr Easy & Barker Streets, Randwick, 2031, Australia E-mail: lorimer.moseley{at}gmail.com
Complex regional pain syndrome (CRPS) occurs after stroke, but most cases develop after peripheral trauma and without evidence of brain trauma. However, CRPS is associated with symptoms that appear similar to those observed in patients suffering from hemispatial neglect. Ten participants (four males) with CRPS of one arm performed temporal order judgements of pairs of vibrotactile stimuli, one delivered to each hand, at one of 10 possible stimulus onset asynchronies, under two conditions: arms held each side of the midline and arms crossed over the midline. Participants released a foot switch to indicate which hand had been stimulated first. The order of conditions was randomized and the foot under which the switch was positioned was counterbalanced. There were two blocks of 150 trials in each condition. The stimulus onset asynchronicity at which the participants were equally likely to select either hand, the point of subjective simultaneity (PSS), was compared between conditions and between those with left or right-sided symptoms. When arms were not crossed, the participants prioritized stimuli from the unaffected limb over those from the affected limb (mean ± SD PSS = 25 ± 7.5 ms) and the magnitude of the PSS strongly related to the degree to which the affected hand was cooler than the unaffected hand (r = 0.942, P < 0.001). When the arms were crossed, the effect was reversed: the participants prioritized stimuli from the affected limb over those from the unaffected limb [PSS = –18 ± 13 ms; main effect of condition F (1, 9) = 98.6, P < 0.001]. There was no effect of the side of symptoms. These results show that CRPS is associated with a deficit in tactile processing that is defined by the space in which the affected limb normally resides, not by the affected limb itself, and which relates to the relative cooling of the affected limb. This pattern is consistent with data from those with hemispatial neglect after stroke and raises the possibility that chronic CRPS involves a type of spatial neglect.
Key Words: Reflex sympathetic dystrophy; temporal order judgments; CRPS; neglect; neuropathic pain
Abbreviations: CRPS, complex regional pain syndrome; JND, just noticeable difference; PSS, point of subjective simultaneity; TOJs, temporal order judgements
Received May 7, 2009. Revised June 28, 2009. Accepted July 15, 2009.