Motor function and motor cortical reorganization in the transition to sustained pain
Schabrun SM, Seminowicz DA
1. School of Science and Health, Western Sydney University, Sydney, Australia
2. Department of Neural and Pain Sciences, University of Maryland School of Dentistry, Baltimore, USA
Altered motor function and aberrant corticomotor plasticity have been identified in chronic musculoskeletal pain conditions (e.g. 1-5). However, it is unknown where in the transition to chronic pain these changes develop. A further question is whether adaptation to pain is consistent within and between individuals. Here we used a human pain model (repeated injection of nerve growth factor into the elbow extensor musculature) to investigate motor function and motor cortical organization (transcranial magnetic stimulation mapping of the representation of the elbow extensor muscles) in individuals as they developed progressively worsening muscle pain lasting up to 14 days. We hypothesized that altered motor function would develop in parallel with the pain trajectory and would be associated with aberrant motor cortical plasticity, but that the direction of change would differ between individuals. In 21 otherwise healthy individuals, we observed two discrete patterns of corticomotor plasticity in response to pain (depression or facilitation of corticomotor excitability) that were consistent within an individual and were associated with altered motor function. The pattern of corticomotor excitability adopted by an individual was related to their pain severity and self-reported disability. These data provide preliminary evidence of individual differences in motor adaptation in response to the development of sustained pain that could be related to an individual’s pain susceptibility.
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