Beta-range cortical motor spectral power and corticomuscular coherence as a mechanism for effective corticospinal interaction during steady-state motor output.

The steady-state motor output, occurring during static force, is characterized by synchronization between oscillatory cortical motor and muscle activity confined to the beta frequency range (15-30 Hz). The functional significance of this beta-range coherence remains unclear. We hypothesized that if the beta-range coherence had a functional role, it would have a behavioral correlate; specifically, it would be related to the precision of the steady-state motor output. To test this hypothesis, we investigated the corticomuscular (EEG-EMG) coherence in eight healthy subjects during steady-state motor output in a visuomotor task, in which the subjects exerted a static force with their right index finger to keep a visual cursor within a target zone. We show that the beta-range EEG-EMG coherence is related to the behavioral performance, i.e. the error signal between target and exerted force. Furthermore, we show that the amplitude of the cortical spectral power is also related to the performance. Moreover, we provide evidence that the EEG-EMG coherence and the cortical spectral power are not completely independent phenomena. Together, our findings indicate that higher beta-range cortical spectral power and increased corticospinal coherence in the beta-range improve motor performance during steady-state motor output. This suggests that the beta-range cortical motor spectral power and corticomuscular coherence may promote effective corticospinal interaction.