ACUTE NOCICEPTION MODIFIES LOW‑DIMENSIONAL BRAIN–MUSCLE NETWORKS DURING REPETITIVE UPPER LIMB ACTIONS

Introduction: Acute pain can alter motor control, yet its effects on brain muscle network (BMN) organization during dynamic upper limb tasks remain unclear. This study aimed to determine how experimentally induced shoulder pain modifies time frequency cortico-muscular and intermuscular coherence, focusing on beta and gamma band activity during repetitive finger pointing.
Methods: Sixteen healthy adults performed a 0.25 Hz pointing task before and after injection of hypertonic saline into the anterior deltoid to induce acute shoulder pain. EEG from C3 and C4 and EMG from 8 upper limb muscles were collected along with kinematic recordings. EMG signals were filtered and Hilbert rectified; EEG underwent band-pass filtering, ICA cleaning, and down sampling. Coherence was estimated using Welch method, and significant coupling was identified using a 95% confidence interval based on repetition count. Time-frequency coherence matrices were decomposed using non-negative matrix factorization, retaining components (i.e., BMNs) that explained at least 5% of variance.
Results & Discussions: Four networks accounting for approximately 72% of coherence variance were identified, and all showed pain related modulation. Networks differed in their phase specific changes throughout the movement cycle, with marked alterations around movement initiation and target reaching. Some networks weighted shoulder muscles more strongly, whereas others emphasized distal muscles, indicating functional specialization. Differences between beta and gamma bands across conditions (baseline vs pain) were present but smaller than differences across networks. Overall, acute shoulder pain reorganized brain muscle networks without impairing task performance, suggesting selective recruitment of existing control structures under nociceptive conditions.