Pain-Induced changes in corticospinal excitability are associated with adaptive changes in muscle coordination

Most pain studies overlook the relationship between corticomotor function changes and coordinated muscle patterns in voluntary movement. A pre-post study was performed to investigate relationships between changes in corticospinal excitability (CSE) and spatial changes in muscle coordination in response to pain. Methods: Thirty pain-free participants performed an upper limb pointing task in pain-free then experimental painful conditions. Transcranial magnetic stimulation was used to assess CSE via the deltoid muscle input-output curves (slope, plateau and S₅₀). Electromyography was used to record trapezius and deltoid muscle activity. Spatial adaptations of muscle coordination to pain were assessed using non-negative matrix factorization (NNMF), comparing the norm of coordination pattern vectors between pain and no-pain conditions, as well as the cosine of the angle between these vectors. Correlations were examined among pain-induced changes in CSE and muscle coordination. Results: Correlations revealed associations between pain-induced S₅₀ change and both pain-induced cosine and norm changes (r_S = 0.43; p = 0.05 for both). Additionally, a correlation was found between pain-induced changes in the coordination pattern's norm and both the IO curve's slope (r_S = -0.46; p = 0.04) and plateau (r_S = 0.45; p = 0.04). Discussion: Overall, this study showed that pain-induced CSE changes were associated with changes in muscle coordination, with participants exhibiting greater CSE changes also showing greater coordination changes.