Elsevier

Neuroscience Letters

Volume 605, 25 September 2015, Pages 7-11
Neuroscience Letters

Research paper
Structured movement representations of a phantom limb associated with phantom limb pain

https://doi.org/10.1016/j.neulet.2015.08.009Get rights and content

Highlights

  • We investigated the relationship between the phantom limb pain (PLP) and its movement representation.

  • We used a bimanual coordination task to evaluate the movement representation.

  • Negative correlation was observed between PLP and the bimanual coupling effect.

  • Structured movement representations of a phantom limb is related with PLP.

Abstract

The relation between phantom limb pain (PLP) and the movement representation of a phantom limb remains controversial in several areas of neurorehabilitation, although there are a few studies in which the representation of phantom limb movement was precisely evaluated. We evaluated the structured movement representation of a phantom limb objectively using a bimanual circle–line coordination task. We then investigated the relation between PLP and the structured movement representation. Nine patients with a brachial plexus avulsion injury were enrolled who perceived a phantom limb and had neuropathic pain. While blindfolded, the participants repeatedly drew vertical lines using the intact hand and intended to draw circles using the phantom limb simultaneously. “Drawing of circles” by the phantom limb resulted in an oval transfiguration of the vertical lines (“bimanual coupling” effect). We used an arbitrary ovalization index (OI) to quantify the oval transfiguration. When the OI neared 100%, the trajectory changed toward becoming more circular. A significant negative correlation was observed between the intensity of PLP and the OI (r = −0.66, p < 0.05). Our findings directly suggest that structured movement representations of the phantom limb are necessary for alleviating PLP.

Introduction

Movement representations of our body are systemically structured through the cognitive process of sensorimotor integration interacting with the surrounding environment [1]. Deafferentation of a limb frequently leads to phantom limb awareness, and patients perceive vivid kinesthesia [2]. The majority of patients perceiving a phantom limb tend to experience decreased awareness of its kinesthesia, but the phantom limb is “recognized” as fixed in one or more peculiar positions [2]. Accompanying phantom limb awareness, patients with a deafferented limb frequently suffer from phantom limb pain (PLP) with maladaptation of central nervous system plasticity [3]. PLP is often resistant to pharmacotherapy, but it responds to some kinds of neurorehabilitation techniques such as mirror visual feedback in association with plastic change of brain [4], [5], [6], [7]. Previous studies demonstrated that PLP patients who restored voluntary movement representation of their phantom limb described PLP alleviation after neurorehabilitation or use of a functional prosthesis [4], [5], [8], [9]. One line of thinking about PLP neurorehabilitation that uses precise visual feedback of phantom limb movements is based on a working hypothesis that incoordination of movement representation of a limb causes pathological pain. However, few reports exist where the representation of a phantom limb's precision of movement was evaluated in behavioral analysis. In the present study, we assessed structured movement representation of a phantom limb objectively using the bimanual circle–line coordination task (BCT) and validated the relation between phantom limb pain and structured movement representation.

Section snippets

Participants

Nine patients, who suffered from a brachial plexus avulsion injury and perceived a phantom limb and its pathological pain, participated in this study (Table 1). All participants were outpatients at our institute with a chief complaint of phantom limb pain. The Ethical Review Board of the Faculty of Medicine, The University of Tokyo approved this study. We explained the content of this study and the purpose to all subjects and obtained their written informed consent.

Quantitative evaluation of the movement representation

The bimanual circles–lines

Results

Comparing the bimanual coupling effect between the dominance group and non-dominance group, there were no significant differences (p = 0.64: dominance group, 2.23 ± 1.41 (mean ± SD); non-dominance group, 1.89 ± 1.88); hand dominance did not seem to influence the bimanual coupling effect. There NRS of pain intensity were 4.78 ± 1.92 (mean ± SD) and the OI scores in each condition were as follows: unimanual condition, 6.01 ± 1.92; Bimanual condition, 8.05 ± 1.85. The bimanual circle–lines coupling showed a

Discussion

The present study was the first attempt to verify the relationship between PLP and its structured movement representation, which is quantitatively evaluated with the BCT. In the present study, the ovalization index in the bimanual condition was higher than that in the unimanual condition [unimanual: 6.01 ± 1.92, bimanual: 8.05 ± 1.85]. This result suggests that the movement representation of a phantom limb remains to some degree, despite patients’ long-term deafferentation. Further, it was revealed

Conclusions

In conclusion, we found an intimate relationship only between the structured movement representations of a phantom limb and its pain. We suggest the importance of evaluating the movement representations in a quantitative way, and that structured movement representations of the phantom limb are necessary for alleviating PLP.

Conflict of interest

The authors report and confirm that there are no conflicts of interest. We alone are responsible for the contents and writing up of our study.

Acknowledgements

The study was supported by a grant from Grants-in-Aid for Scientific Research on Innovative Areas ”Constructive Developmental Science and Grant-in-Aid for Young Scientists (B).

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