Do people with chronic pain have altered motor imagery?

The left/right judgement task (LRJT) is a common method of assessing motor imagery performance. The LRJT  involves viewing images of a hand or foot [1], for example, and determining whether the image belongs to the left or right side of the body. This determination is done implicitly meaning that we make an initial judgement then mentally position our “virtual hand” to match the image seen. The time taken to make this automatic ‘online’ movement is similar to that for the corresponding physical movement. Interestingly, biomechanical constraints that apply to our physical movements also seem to apply to our imagined movements, and awkward movements take longer than simpler movements. Increased response times reflect delayed central processing. Poor accuracy for the task is thought to reflect disrupted cortical body part representations. The task has been adapted for different parts of the body including back [2] and necks [3], shoulders [4] and the face [5].

Researchers have investigated the LRJT in a number of painful conditions affecting the musculoskeletal system including complex regional pain syndrome (CRPS)[6], chronic limb pain [7], osteoarthritis [8], and back pain [9] amongst others. Alterations in motor imagery have been reported in some of these studies suggesting that central changes may be associated with these conditions. There is a further suggestion that these central changes may contribute to the maintenance of chronic pain and treatments aimed at reversing these changes have shown some promise [10].

Recently, we conducted a comprehensive systematic review of the literature to determine whether motor imagery impairment, as measured by the LRJT, is a characteristic feature of all chronic musculoskeletal conditions [11]. From eight databases and over 7000 citations, 25 studies met our final inclusion criteria. The included studies comprised 13 different chronic musculoskeletal pain conditions which were then divided based on diagnosis or region of pain; CRPS, upper limb pain, lower limb pain, facial pain, neck pain, and low back pain. Together, these studies included a total of 2,266 participants.

What did we find? Overall, chronic musculoskeletal pain was associated with poorer motor imagery performance. In general, people with chronic musculoskeletal pain were slower and less accurate at the LRJT than painfree healthy people.  People with chronic pain were also slower and less accurate at recognising images that corresponded to their painful side. But there were also interesting subgroup differences between peripheral (limbs and face) and trunk (neck and back) conditions. People with peripheral pain conditions including CRPS, limb pain, and facial pain were slower and less accurate than healthy people, and they were slower and less accurate with images that corresponded to their painful body part. In contrast, people with neck pain were no different to healthy people at the LRJT, and people with back pain were no different in speed at the task, but were less accurate, than healthy people.

This systematic review found that motor imagery performance as measured by the LRJT, was altered in chronic musculoskeletal pain conditions. These findings were consistent in peripheral conditions but not so in trunk conditions and the implications are that the central processes required for successful motor imagery are impaired in the presence of chronic peripheral pain. Why so?

Perhaps the peripheral LRJTs are more sensitive to change. Perhaps the limb LRJTs involve greater virtual movement that does trunk LRJTs and therefore greater central processing resources than a trunk LRJT, reflected in longer response times which would in turn make them more sensitive to change. Perhaps trunk LRJTs were less consistent because neck and back pain is less consistently lateralised. Neck pain, for example, can be left sided, right sided, central or bilateral. Left sided movement of the neck may produce left side pain, or right side pain or both. This contrariness may be reflected in the inconsistent trunk LRJT findings. Conversely, peripheral pain tends to be more constantly lateralised – it would be unlikely for movements of the right wrist to result in left wrist pain. Or perhaps some of the trunk LRJTs in their current form may not be true motor imagery tasks, an argument that has been put forward on this blog previously by David Punt. Alternatively, the subgroup differences we found could be due to variability in, and the relatively small number of studies of trunk conditions. Lastly, bias related to convenience sampling, assessor non-blinding, and the small sample size of some of the included studies could have contributed to these subgroup differences.

That said, the consistency of this result across peripheral conditions would suggest that alteration in motor imagery is a common feature of all such conditions.

About John David Breckenridge

John is an Australian Physiotherapist who specialises in upper limb conditions and splits his time between clinical and research work.

He is completing his PhD focussing on perceptual changes in people shoulder pain, including motor imagery, left/right judgement and two point discrimination

References

[1] Parsons LM. Imagined spatial transformations of one’s hands and feet. Cogn Psychol. 1987;19(2):178-241.

[2] Bray H, Moseley GL. Disrupted working body schema of the trunk in people with back pain. British journal of sports medicine. 2011;45(3):168-73.

[3] Wallwork SB, Butler DS, Fulton I, Stewart H, Darmawan I, Moseley GL. Left/right neck rotation judgments are affected by age, gender, handedness and image rotation. Manual therapy. 2013;18(3):225-30.

[4] Breckenridge JD, McAuley JH, Butler DS, Stewart H, Moseley GL, Ginn KA. The development of a shoulder specific left/right judgement task: Validity & reliability. Musculoskelet Sci Pract. 2017;28:39-45.

[5] von Piekartz H, Wallwork SB, Mohr G, Butler DS, Moseley GL. People with chronic facial pain perform worse than controls at a facial emotion recognition task, but it is not all about the emotion. Journal of oral rehabilitation. 2015;42(4):243-50.

[6] Moseley GL. Why do people with CRPS take longer to recognize their affected hand? Neurology. 2004;62:2182-6.

[7] Coslett HB, Medina J, Kliot D, Burkey AR. Mental motor imagery indexes pain: the hand laterality task. European journal of pain. 2010;14(10):1007-13.

[8] Stanton TR, Lin CW, Smeets RJ, Taylor D, Law R, Moseley GL. Spatially defined disruption of motor imagery performance in people with osteoarthritis. Rheumatology. 2012;51(8):1455-64.

[9] Bowering KJ, Butler DS, Fulton IJ, Moseley GL. Motor imagery in people with a history of back pain, current back pain, both, or neither. The Clinical journal of pain. 2014;30(12):1070-5.

[10] Moseley GL, Flor H. Targeting Cortical Representations in the Treatment of Chronic Pain: A Review. Neurorehabilitation and Neural Repair. 2012;26(6):646-52.

[11] Breckenridge JD, Ginn KA, Wallwork SB, McAuley JH. Do People With Chronic Musculoskeletal Pain Have Impaired Motor Imagery? A Meta-analytical Systematic Review of the Left/Right Judgment Task. J Pain. 2018.