Corticomuscular Coherence with Low-Level Forces

The present study was aimed at investigating the corticomuscular synchronization in beta- (15-30 Hz) and gamma-range (30-45 Hz) during isometric compensation of low-level forces. It is still unknown to what extent the synchronization processes in these frequency ranges can coexist or influence each other when the static component only is modulated in a dynamic stimulation pattern. We investigated the corticomuscular coherence (CMC), as well as the cortical spectral power (SP) during a visuomotor task, where 8%, 16% and 24% of the maximal voluntary contraction (MVC) were used. Seven healthy right-handed female subjects compensated isometrically the different dynamic forces with their right index finger. EEG was recorded from 52 scalp positions and belly-tendon bipolar EMG from the first dorsal interosseus muscle (FDI). Under the three conditions investigated, the beta- and gamma-range CMC existed in parallel. They behaved in a different manner: while the beta-range coherence increased linearly during higher force application, the gamma-range CMC was not significantly modulated by the force levels. Our results suggest that although gamma-range CMC is functionally associated to the isometric compensation of dynamic forces, broad beta-range CMC can fulfill functions of motor control simultaneously different when low-level forces are applied.