Beta bursts in SMA mediate anticipatory muscle inhibition.

In motor networks, inhibition has been associated with oscillatory activity in the mu (8 to 12 Hz) or beta (13 to 30 Hz) bands, yet how these rhythms ultimately influence muscle activity remains 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 in adult participants performing the BLLT. Optimal postural stabilization occurred when biceps brachii inhibition preceded unloading by ~10 to 40 ms. Stronger muscle inhibition within this time window was associated with reduced high-gamma (90 to 130 Hz) power, potentially reflecting reduced excitability, 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 to 28 Hz) exhibited both optimally timed anticipatory inhibition and concurrent reduction in high-gamma power. These findings suggest that optimal anticipatory inhibition in the load-supporting elbow flexor is linked to reduced SMA excitability mediated by inhibitory beta bursts. More broadly, they provide new evidence linking beta bursts to the inhibitory control of muscle function and contribute to a better understanding of motor anticipation.