Motor actions are planned and steered from the brain. Input from eyes, muscles, joints, skin and vestibular system continuously inform the brain about actual movements. Simultaneously, this information is compared with the motion program (that what was predicted) in the brain, which is important for adjusting motor plans and ensuring smoothness of motor action. This process is normal automatic and implicit, but we can made aware of it when incongruence exists between that what the brain predicted to do (the motion program) and that what really occurred. This may lead to the experience of pain and other sensations, in the same way as a conflict between visual and vestibular input may result in motion sickness.
In a recently published paper in Rheumatology, we investigated the hypothesis that pain results from incongruence between predicted and actual sensory feedback. Interestingly, we found that inducing sensorimotor incongruence by manipulating the visual input resulted in the experience of sensations such as loss of control, feeling of peculiarity, weight changes and discomfort, but not pain, in healthy subjects. These findings confirm the notion that sensorimotor incongruence can induce sensations, however, are in contrast with the aspect of the cortical pain model proposing that sensorimotor incongruence elicits pain.
In patients with chronic whiplash associated disorders (WAD), reducing or disturbing the visual input (via hiding a moving limb) seemed to be sufficient to exacerbate symptoms and/or elicit additional sensations. No additional effect was observed when visual input (manipulated by using a mirror) conflicts with proprioceptive feedback. These findings suggest that patients with chronic WAD rely heavily on visual input of neck and upper limbs to reassure the brain about movements. In addition, the results indicate altered perception of distorted visual feedback and support the presumption of body schema disruption in chronic WAD. Disturbing the visual input can further modify the body schema and hence, modulate pain and other sensations. Following this, therapy strategies which intend to restore the visual input and improve the sensorimotor integration at cortical level may lead to symptom relief in chronic WAD. Although further research is warranted to examine these assumptions.
In conclusion, our work shows that sensorimotor incongruence can generate sensations, but not pain, in healthy subjects and that reducing or disturbing the visual input is sufficient to exacerbate symptoms in patients with chronic WAD. Although the mechanism underpinning the abovementioned observations and its role in the development and/or maintenance of pain and other symptoms remains to be revealed and hence, requires further study. More in-depth understanding of it may help to improve treatment strategies.
About Liesbeth Daenen
Liesbeth Daenen is a doctoral researcher at the University of Antwerp (Belgium) and the Vrije Universiteit Brussel (Belgium). She is interested in the role of central mechanism and their interaction in (chronic) unexplained pain. Her work focuses on changes in sensorimotor integration and pain processing mechanisms and, pain-motor interactions in patients with whiplash associated disorders.
Reference
Daenen L, Nijs J, Roussel N, Wouters K, Van Loo M, & Cras P (2012). Sensorimotor incongruence exacerbates symptoms in patients with chronic whiplash associated disorders: an experimental study. Rheumatology (Oxford, England), 51 (8), 1492-9 PMID: 22525161