Beta bursts in SMA mediate anticipatory muscle inhibition

In motor networks, inhibition has been associated with oscillatory activity in the mu (8-12Hz) or beta (13-30Hz) bands, yet the mechanisms by which they exert influence at the muscular level remain unclear. The Bimanual Load-Lifting Task (BLLT) elicits anticipatory inhibition of the elbow flexors in the load-supporting arm during voluntary load-lifting, providing a suitable model to study oscillatory mechanisms of muscle inhibition. We recorded magnetoencephalography (MEG) in adult participants performing the BLLT. Optimal postural stabilization occurred when Biceps brachii inhibition preceded unloading by ∼30 ms. Stronger muscle inhibition in this window was associated with reduced excitability, indexed by high-gamma (90-130Hz) power, and increased high-beta power in the contralateral Supplementary Motor Area (SMA), with high-gamma power reduction partially mediating the effect of high-beta power on anticipatory inhibition. Furthermore, trials containing beta bursts (22-28Hz) exhibited optimally timed anticipatory inhibition and a concurrent reduction in high-gamma power. Our data indicate that optimal anticipatory inhibition in the load-supporting elbow flexor is achieved through SMA suppression mediated by inhibitory beta bursts. To our knowledge, these results provide the first evidence that beta bursts can exert direct inhibitory control over muscle function, while advancing understanding of motor anticipation and informing future clinical and developmental studies.