Impaired spatial body representation in CRPS I

Imagine being offered one half of a Snickers Bar that on first glance was cut into two equal halves. Unless a machine bisected it, the right half would still be just a tiny bit larger. Why is that? Roughly said, the brain’s hemispheres are responsible for different functions. The right hemisphere is specialized in spatial abilities. When asked to bisect a line, humans tend to bisect it more to the left of its veridical centre, a phenomenon that is presumed to result from the right-hemispheric dominance in spatial tasks [1,2].

This phenomenon is called “Pseudoneglect” and also occurs when you draw an imaginary line through the midst of your body, a body midline so to say[2]. Why would I do that, you might ask?  Well, similar to a GPS, the brain uses spatial coordinate frames to encode the location of objects in space. Just like a GPS, the brain needs reference frames to encode space and the body midline functions as a reference for what scientist call the egocentric reference frame [3]. When our brain encodes the position of objects in relation to the body, it does so in an egocentric reference frame. Interestingly, the egocentric reference frame is closely related to the body schema which is a sort of body representation in the brain that (among other things) informs you about the position of your body and body parts in space [3].

It is well-known nowadays that the brain’s representation of the body is changed in chronic neuropathic pain and in fact, chronic pain patients often have distortions of the body schema. This is particularly the case in patients with complex regional pain syndrome (CRPS I). Imaging studies have shown that the brain’s representation of the painful hand is changed in CRPS and these alterations in the central nervous system (CNS) are presumably linked to the distortions of the body schema [4]. But are distortions of the body schema also related to distorted spatial abilities in chronic pain?

To examine this, we asked patients with CRPS on the hand, patients with pain of other origin than CRPS on the hand and healthy subjects to visually position their body midline. The task was carried out in the light and in the dark so that in the dark, participants would have to rely on their body schema when estimating their body midline. We found that in the dark, CRPS patients positioned their body midline significantly farther away from the objective body midline. And although all other participants positioned their bodymidline slightly towards the left from the veridical centre as well (remember Pseudoneglect), the amount of leftward deviation was largest in CRPS patients. This told us 2 things: a) only CRPS patients are impaired to encode the position of objects in relation to their body midline and b) it appears that not chronic pain per se but rather the CRPS-associated CNS changes in regions responsible for the body schema underlie this distorted visuo-spatial perception. Thus, the CRPS-asscoiated CNS changes that are involved in the distortion of the body schema also underlie the CRPS-specific distortion of visuo-spatial perception. Moreover, in CRPS these CNS changes appear to cause an accentuation of the leftwards bias (Pseudoneglect) that is presumed to result from the right-hemispheric dominance in spatial tasks [5]. Future research should focus on the close relation between the body schema and visuo-spatial perception in CRPS.

About Annika Reinersmann

grey Impaired spatial body representation in CRPS IAnnika did her Masters of Psychology at Nijmegen University in the Netherlands. Her PhD project was a collaboration between the Department of Pain Management and the Institute of Cognitive Neuroscience, Biopsychology at Ruhr-University Bochum.  Annika’s research interests are in the neural correlates of the body schema & the interaction between body schema and body image in chronic pain.

References

[1] Jewell G, & McCourt ME (2000). Pseudoneglect: a review and meta-analysis of performance factors in line bisection tasks. Neuropsychologia, 38 (1), 93-110 PMID: 10617294

[2] Birch HG, Proctor F, Bartner M, Lowenthal M (1960). Perception in hemiplegia: II. Judgment of the median plane. Arch Phys Med Rehabil 41, 71-5 PMID: 13800837

[3] Galati, G., Pelle, G., Berthoz, A., & Committeri, G. (2010). Multiple reference frames used by the human brain for spatial perception and memory Exp Brain Res 206 (2), 109-120 DOI: 10.1007/s00221-010-2168-8

[4] Schwenkreis P, Maier C, & Tegenthoff M (2009). Functional imaging of central nervous system involvement in complex regional pain syndrome. AJNR. Am J Neuroradiol, 30 (7), 1279-84 PMID: 19386737

[5] Reinersmann A, Landwehrt J, Krumova EK, Ocklenburg S, Güntürkün O, & Maier C (2012). Impaired spatial body representation in complex regional pain syndrome type 1 (CRPS I). Pain, 153 (11), 2174-81 PMID: 22841878

Comments

  1. Fascinating ! Was there any fluctuation in leftwards bias depending on affected hand ? As you know, there is tons of evidence that cortical representation of the affected limb in CRPS has undergone significant changes. With GMI, is there another reason why lateralization as an initial step helps ? My understanding of the proposed view is that initial (re)activation of cortical networks that involve representation of the limb and preparation for movement (pre-motor cortex) are critical prior to activating primary sensory and motor cortices (with imagined movements and mirror use) for reorganization of altered somatosensory cortex especially with chronic CRPS. Does lateralization help in any way with restoring patient’s perception of midline ? Does it activate right or left pre-motor cortex (or both) depending on affected side ? Thanks for the research ! Still curious.

  2. Reta Russell-Houghton says:

    This is all very interesting but what practical purpose does it serve? How will this help a person like myself with CRPS type 1 in my left arm.

    Annika Reply:

    Dear Reta,
    although the aim of medicine – and other curative sciences – is to heal disease, it is difficult to do so without understanding the underlying pathogenesis and pathophysiology of a given syndrome. The practical purpose of this study may not be immediately observable but in adding to the understanding of the way that CRPS pathophysiology may contribute to the disruption of body representation and perception we hope to contribute to the development of effective treatment options for CRPS.

  3. Hi Reta – although I’ll wait for more feedback from the researchers and experts out there, the importance of research like this illustrates that there is altered perception with CRPS – if you can reverse this altered perception you can help reduce pain (in some studies, use of prisms to alter visual perception of affected limb has reduced pain; in other studies mirror therapy used early in treatment has helped and in later cases, graded motor imagery has shown to be beneficial). Even crossing arms past midline has reduced pain with CRPS in studies. However, for me, like you, I am looking for more clarity about this study and its practical implications and am hopeful for further insight. Thanks.

  4. Dear Stuart, unfortunately the effects of lateralisation on setting the body midline have not yet been explored. A japanese research group found prims adaptation to be effective in reversing the body midline shift – which was also accompanied by some alleviation of the pain. The practical impact of fundamental research projects often is more its benefit in clarifying underlying pathomechanisms. To this regard, being able to identify vision as closely related to pain, which previously was shown to be closely connected to body perception may help, as you said, in improving existing treatment interventions or even develop new ones.

  5. Reta Russell-Houghton says:

    I’ll wait and see what comes of this.

  6. stuart miller says:

    Annika, thank you for providing some clarity with your article. I realize there is right hemispheric lateralization for spatial awareness. It is rare to see a patient with right hemispatial neglect (I do see patients with brain injuries with diffuse damage in their brain with decreased awareness of the right side but ? the right side of space). I can sort of see how only perceiving the right side of space happens but not how hyper protection or hyper vigilance happens on the affected side with CRPS unless the body schema is more determined sub cortically (?insular cortex/operculum and other areas). Could you help me with understanding ? Could you also explain egocentric and allocentric reference ? Thanks a lot for your work !