High-frequency cortical neural inputs to muscles during movement cancellation

Cortical beta (13-30 Hz) and gamma (30-60 Hz) oscillations have been investigated during motor processing. Although they are at frequencies greater than the dynamic bandwidth of muscle contraction, these oscillations are partly transmitted from the cortex to motoneurons and muscles. Little is known about when and why this transmission occurs. We developed an experimental approach to examine these high frequency inputs to motoneurons under different motor states while maintaining a stable force, thus constraining behaviour. We acquired brain and muscle activity during a ‘GO’/’NO-GO’ task. In this experiment, the effector muscle for the task (tibialis anterior) was kept tonically active during the trials, while participants (N=9) reacted to sequences of auditory stimuli by either keeping the contraction unaltered (‘NO-GO’ trials), or by quickly performing a ballistic contraction (‘GO’ trials). Motor unit (MU) firing activity was extracted from high-density surface and intramuscular electromyographic signals, and the changes in its spectral contents in the ‘NO-GO’ trials were analysed. We observed an increase in beta and low-gamma (30-45 Hz) activity post ‘NO-GO’ cue at the brain and muscle levels. There was also an increase in the activity within 8-12 Hz, which was only observed at the muscle level. Overall, our results suggest that the cortical processing of movement cancellation occurs at least in part via increased power of high-frequency oscillations transmitted downstream to the muscles. These changes occur without alterations in behaviour, suggesting that the downstream transmission of these high-frequency oscillations does not have a direct functional impact.